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Lipid profile
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| Lipid profile | |
|---|---|
| MeSH | - |
| MedlinePlus | 003491 |
| eMedicine | - |
| LOINC | 24331-1, 57698-3 |
A lipid profile or lipid panel is a panel of blood tests used to find abnormalities in blood lipid ( such as cholesterol and triglycerides) concentrations.[not verified in body] The results of this test can identify certain genetic diseases and can determine approximate risks for cardiovascular disease, certain forms of pancreatitis, and other diseases.
Lipid panels are usually ordered as part of a physical exam, along with other panels such as the complete blood count (CBC) and basic metabolic panel (BMP).[not verified in body]
Components
[edit]A lipid profile report typically includes:[1]
- Low-density lipoprotein (LDL)
- High-density lipoprotein (HDL)
- Total triglycerides
- Total cholesterol
LDL is not usually actually measured, but calculated from the other three using the Friedewald equation.[1] A laboratory can optionally calculate the two extra values from the report:
- Very low-density lipoprotein (VLDL)
- Cholesterol:HDL ratio
Procedure and indication
[edit]Recommendations for cholesterol testing come from the Adult Treatment Panel (ATP) III guidelines, and are based on many large clinical studies, such as the Framingham Heart Study.[citation needed]
For healthy adults with no cardiovascular risk factors, the ATP III guidelines recommend screening once every five years.[2] A lipid profile may also be ordered at regular intervals to evaluate the success of lipid-lowering drugs such as statins.[citation needed]
In the pediatric and adolescent population, lipid testing is not routinely performed. However, the American Academy of Pediatrics and the National Heart, Lung, and Blood Institute (NHLBI) recommend that children aged 9–11 be screened once for severe cholesterol abnormalities.[3] This screening can be valuable to detect genetic diseases such as familial hypercholesterolemia that can be lethal if not treated early.[citation needed]
Traditionally, most laboratories have required patients to fast for 9–12 hours before screening. However, studies have questioned the utility of fasting before lipid panels, and some diagnostic labs routinely accept non-fasting samples.[4][5][6][7]
Methods
[edit]Friedewald
[edit]Typically the laboratory measures only three quantities: total cholesterol; HDL; Triglycerides. A typical procedure used by NHANES 2004 uses the following measurement methods:[8]
- Total cholesterol is measured using a mixture of enzymes. First an esterase converts cholesterol esters into cholesterol and free fatty acid. Then an oxidase oxidizes the cholesterol, producing a H2O2 side-product that changes the color of a dye. The amount of oxidation can be precisely quantified by light absorbance at 500 nm.[8]
- Triglyceride concentration is also measured using an enzyme mixture. A lipase releases glycerol from the molecules, which gets oxidized by another enzyme while producing H2O2. The same color-change follows.[8]
- HDL is measured in two steps. First a special reagent is added to the serum that binds apoB-containing lipoprotein particles, shielding them from the enzymes in the next step. Then a mixture of PEGylated enzymes is added with dye. The chemical reaction is the same as the total cholesterol measurement, except that the enzymes are blocked from acting on non-HDL lipoproteins by the reagent and their own PEG tails.[8]
From these three data LDL may be calculated. According to Friedewald's equation:[9]
- [LDL] = [Total cholesterol] − [HDL] − [Triglycerides] /5
Other calculations of LDL from those same three data have been proposed which yield some significantly different results.[10]
VLDL can be defined as the total cholesterol that is neither HDL nor LDL. With that definition, Friedewald's equation[9] yields:
- [VLDL] = [Triglycerides] /5
The alternative calculations mentioned above may yield significantly different values for VLDL.
The Friedewald method is reasonably reliable for the majority of patients, but is notably inaccurate in patients with hypertriglyceridemia (> 400 mg/dL or 4.5 mmol/L). It also underestimates LDL-C in patients with low LDL-C (< 25 mg/dL or 0.6 mmol/L). It does not take into account intermediate-density lipoprotein.[1]
A "Martin/Hopkins" variation that takes into how triglycerides-to-VLDL ratio tends to vary with other parameters appears more reliable and accurate.[11][12][13]
All-direct
[edit]Every part of the lipid panel can be measured directly using ultracentrifugation, which is the gold standard.[1] This type of measurement involves no errors from estimation and can also measure IDL-C and Lp(a)-C levels. Fully direct measurement is more costly, however.[14]
Laboratories may also use proprietrary tests for "direct chemical LDL-C" which require no prior separation by centrifugation. These tests are not yet standardized in US and Europe and lack validation.[13] A specific version of the test seems popular in Japan, however.[15] A number of other LDL-C determination methods have been used in the past or have been proposed for future use.[16]
Implications
[edit]This test is used to identify dyslipidemia (various disturbances of cholesterol and triglyceride levels), many forms of which are recognized risk factors for cardiovascular disease and rarely pancreatitis.
A total cholesterol reading can be used to assess an individual's risk for heart disease; however, it should not be relied upon as the only indicator. The individual components that make up total cholesterol reading—LDL, HDL, and VLDL—are also important in measuring risk.[citation needed]
For instance, someone's total cholesterol may be high, but this may be due to very high HDL ("good cholesterol") cholesterol levels,—which can help prevent heart disease (the test is mainly concerned with high LDL, or "bad cholesterol" levels). So, while a high total cholesterol level may help give an indication that there is a problem with cholesterol levels, the components that make up total cholesterol should also be measured.[citation needed]
Lipid Profiling in Diabetes Risk Prediction
[edit]A study by King's College London identified a novel blood test using lipid profiling to predict diabetes risk in children. Researchers found that lipid molecules in blood plasma could serve as early indicators for metabolic diseases, including type 2 diabetes, liver disease, and heart complications, even independent of obesity levels.[17]
References
[edit]- ^ a b c d Lee Y, Siddiqui WJ (2023). "Cholesterol Levels". StatPearls. StatPearls Publishing. PMID 31194434.
- ^ Grundy, S.M., et al. (Expert Panel on Detection / National Cholesterol Education Program (NCEP)) (2002). "Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report". Circulation. 106 (25): 3143–3421. doi:10.1161/circ.106.25.3143. hdl:2027/uc1.c095473168. PMID 12485966.
- ^ "Pediatric cardiovascular risk reduction guidelines – NHLBI, NIH". Archived from the original on 2012-11-16.
- ^ Sidhu D, Naugler C (2012). "Fasting time and lipid levels in a community-based population: A cross-sectional study". Archives of Internal Medicine. 172 (22): 1–4. doi:10.1001/archinternmed.2012.3708. PMID 23147400.
- ^ Nordestgaard BG, Langsted A, Mora S, Kolovou G, Baum H, Bruckert E, et al. (July 2016). "Fasting is not routinely required for determination of a lipid profile: Clinical and laboratory implications including flagging at desirable concentration cut-points – a joint consensus statement from the European Atherosclerosis Society and European Federation of Clinical Chemistry and Laboratory Medicine". Eur. Heart J. 37 (25): 1944–1958. doi:10.1093/eurheartj/ehw152. PMC 4929379. PMID 27122601.
- ^ Mora S (July 2016). "Nonfasting for routine lipid testing: From evidence to action". JAMA Intern Med. 176 (7): 1005–1006. doi:10.1001/jamainternmed.2016.1979. PMID 27119719.
- ^ Anderson LN, Maguire JL, Lebovic G, Hanley AJ, Hamilton J, Adeli K, et al. (January 2017). "Duration of fasting, serum lipids, and metabolic profile in early childhood". The Journal of Pediatrics. 180: 47–52.e1. doi:10.1016/j.jpeds.2016.09.005. ISSN 0022-3476. PMID 27742126. S2CID 8691354. Retrieved 17 November 2020.
- ^ a b c d "Laboratory Procedure Manual; Total Cholesterol, HDL-Cholesterol, Triglycerides, and LDL-Cholesterol; Serum; Hitachi 704" (PDF). cdc.gov.
- ^ a b Friedewald WT, Levy RI, Fredrickson DS (1972). "Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge". Clin. Chem. 18 (6): 499–502. doi:10.1093/clinchem/18.6.499. PMID 4337382;
cited in "[title not cited]". Clin. Chem. 36: 15–19. 1990. - ^ "Calculating your cholesterol". Johns Hopkins Medicine (hopkinsmedicine.org). Johns Hopkins School of Medicine. 3 November 2021.
- ^ Martin SS, Blaha MJ, Elshazly MB, Toth PP, Kwiterovich PO, Blumenthal RS, Jones SR (20 November 2013). "Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile". JAMA. 310 (19): 2061–8. doi:10.1001/jama.2013.280532. PMC 4226221. PMID 24240933.
- ^ Martin SS, Giugliano RP, Murphy SA, Wasserman SM, Stein EA, Ceška R, López-Miranda J, Georgiev B, Lorenzatti AJ, Tikkanen MJ, Sever PS, Keech AC, Pedersen TR, Sabatine MS (1 August 2018). "Comparison of Low-Density Lipoprotein Cholesterol Assessment by Martin/Hopkins Estimation, Friedewald Estimation, and Preparative Ultracentrifugation: Insights From the FOURIER Trial". JAMA Cardiology. 3 (8): 749–753. doi:10.1001/jamacardio.2018.1533. PMC 6143070. PMID 29898218.
- ^ a b Sajja A, Park J, Sathiyakumar V, Varghese B, Pallazola VA, Marvel FA, Kulkarni K, Muthukumar A, Joshi PH, Gianos E, Hirsh B, Mintz G, Goldberg A, Morris PB, Sharma G, Blumenthal RS, Michos ED, Post WS, Elshazly MB, Jones SR, Martin SS (1 October 2021). "Comparison of Methods to Estimate Low-Density Lipoprotein Cholesterol in Patients With High Triglyceride Levels". JAMA Network Open. 4 (10): e2128817. doi:10.1001/jamanetworkopen.2021.28817. PMC 8554644. PMID 34709388.
- ^ Martin SS, Blaha MJ, Elshazly MB, Toth PP, Kwiterovich PO, Blumenthal RS, Jones SR (20 November 2013). "Comparison of a novel method vs the Friedewald equation for estimating low-density lipoprotein cholesterol levels from the standard lipid profile". JAMA. 310 (19): 2061–8. doi:10.1001/jama.2013.280532. PMC 4226221. PMID 24240933.
- ^ Kamezaki F, Sonoda S, Nakata S, Otsuji Y (2010). "A Direct Measurement for LDL-Cholesterol Increases Hypercholesterolemia Prevalence : Comparison with Friedewald Calculation". Journal of UOEH. 32 (3): 211–220. doi:10.7888/juoeh.32.211. PMID 20857815.
- ^ Islam S, Osa-Andrews B, Jones PM, Muthukumar AR, Hashim I, Cao J (December 2022). "Methods of Low-Density Lipoprotein-Cholesterol Measurement: Analytical and Clinical Applications". EJIFCC. 33 (4): 282–294. PMC 9768618. PMID 36605300.
- ^ "New Blood Test Predicts Diabetes Risk in Children". The Hawk. Retrieved 16 February 2025.
Further reading
[edit]- Talwalkar PG, Sreenivas CG, Gulati A, Baxi H (July 2013). "Journey in guidelines for lipid management: From adult treatment panel (ATP)-I to ATP-III and what to expect in ATP-IV". Indian J Endocrinol Metab. 17 (4): 628–635. doi:10.4103/2230-8210.113753. PMC 3743362. PMID 23961478.
Lipid profile
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Definition
A lipid profile, also known as a lipid panel, is a blood test panel that measures the concentrations of key lipids in the bloodstream, including cholesterol fractions and triglycerides, to detect potential abnormalities associated with cardiovascular risk. This diagnostic tool provides a snapshot of lipid metabolism by quantifying total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides from a single blood sample.[6][7] The lipid profile evolved from early 20th-century basic cholesterol tests, with significant advancements occurring in the mid-20th century through the development of enzymatic assays. These assays, first introduced for cholesterol measurement in the early 1970s, enabled precise quantification and were standardized for clinical use in the 1970s, supplanting prior chemical methods and facilitating widespread adoption in routine laboratory practice.[8][9] In contrast to full lipidomics analysis, which uses mass spectrometry to comprehensively profile hundreds of lipid species for research into metabolic pathways, the lipid profile targets only established clinical markers for practical diagnostic purposes.[10][11]Clinical Purpose
The lipid profile serves as a critical screening tool for assessing cardiovascular disease (CVD) risk in clinical practice, by evaluating levels of total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides, which contribute to atherosclerosis and plaque buildup in arteries.[12] Elevated LDL-C and triglycerides, along with low HDL-C, are established predictors of coronary artery disease, heart attack, and stroke, enabling early intervention through lifestyle modifications or pharmacotherapy.[1] Additionally, it screens for acute risks such as pancreatitis, particularly when triglycerides exceed 500 mg/dL (5.6 mmol/L), and identifies genetic disorders like familial hypercholesterolemia (FH), where LDL-C levels often surpass 190 mg/dL in untreated cases, prompting cascade screening in families.[1][12] In line with updated guidelines, the 2018 American Heart Association (AHA)/American College of Cardiology (ACC) recommendations advocate universal lipid screening for all adults aged 20 years and older using either fasting or nonfasting profiles, with repeat testing every 4 to 6 years for those at low 10-year atherosclerotic CVD (ASCVD) risk, and more frequent intervals (e.g., annually) for higher-risk individuals based on factors like diabetes, hypertension, or family history.[12] This approach integrates the Pooled Cohort Equations for precise risk stratification in adults 40 to 75 years, facilitating shared decision-making on statin therapy.[12] In contrast, the 2002 Adult Treatment Panel III (ATP III) guidelines from the National Cholesterol Education Program recommended fasting lipoprotein profiles every 5 years for adults over 20, with less emphasis on lifetime risk assessment or nonfasting options.[13] Lipid profiles are routinely combined with other standard tests, such as the complete blood count (CBC) or comprehensive metabolic panel (CMP), during annual wellness examinations to holistically evaluate metabolic health, detect comorbidities, and guide preventive care.[7] Abnormalities in lipid levels, such as dyslipidemia, further inform CVD risk but are interpreted alongside components detailed elsewhere.[12]Components
Total Cholesterol
Total cholesterol represents the overall concentration of cholesterol in the blood plasma, comprising both free (unesterified) cholesterol and cholesteryl esters transported via various lipoproteins.[14] This measurement captures the aggregate cholesterol content without distinguishing between lipoprotein carriers, providing a foundational assessment of lipid status in clinical evaluations.[15] In laboratory settings, total cholesterol is quantified using an enzymatic colorimetric assay as the reference method, where cholesteryl esters are first hydrolyzed to free cholesterol and then oxidized by cholesterol oxidase to generate hydrogen peroxide, which reacts to produce a quantifiable color change.[16] This assay is widely adopted for its accuracy, precision, and automation compatibility in routine lipid profiling.[17] As a biomarker, total cholesterol serves as an indicator of the body's overall cholesterol load and is associated with cardiovascular disease risk, with elevated levels (typically above 200 mg/dL) signaling potential hypercholesterolemia.[2] However, its interpretive value is limited compared to fractionated analyses, as it does not isolate protective or atherogenic components.[18] Total cholesterol also contributes to the calculation of low-density lipoprotein cholesterol via the Friedewald equation.[19]High-Density Lipoprotein Cholesterol
High-density lipoprotein (HDL) is a type of lipoprotein characterized by its high density and elevated protein content, primarily consisting of apolipoproteins such as apoA-I, which constitutes about 70% of its protein mass.[20] These particles are small, discoidal or spherical in shape, with a core of cholesteryl esters and triglycerides surrounded by a phospholipid monolayer and apolipoproteins that facilitate lipid binding and transport.[21] Unlike other lipoproteins, HDL has a lower lipid-to-protein ratio, enabling its role in cholesterol mobilization from peripheral tissues.[20] The primary function of HDL is reverse cholesterol transport, wherein it acquires free cholesterol from macrophages and other cells in arterial walls via the ATP-binding cassette transporter A1 (ABCA1), esterifies it through lecithin-cholesterol acyltransferase (LCAT), and delivers it to the liver for excretion or recycling.[21] This process helps prevent the accumulation of cholesterol in atherosclerotic plaques, thereby exerting anti-atherogenic effects.[22] HDL also exhibits antioxidant, anti-inflammatory, and antithrombotic properties that contribute to vascular protection.[23] HDL cholesterol is typically measured in clinical laboratories using either precipitation methods, where non-HDL lipoproteins are selectively precipitated with agents like dextran sulfate or phosphotungstate to isolate HDL for enzymatic quantification, or direct homogeneous enzymatic assays that employ detergents to selectively solubilize HDL without precipitation.[24] These methods ensure accurate determination of HDL-C levels, which are reported in milligrams per deciliter (mg/dL) as part of a standard lipid profile.[24] Clinically, HDL cholesterol is often referred to as "good" cholesterol due to its inverse association with cardiovascular disease (CVD) risk, with higher levels generally conferring protection against atherosclerosis and coronary artery disease.[25] According to guidelines from the National Cholesterol Education Program, HDL-C levels below 40 mg/dL in men and 50 mg/dL in women are considered low and represent a major risk factor for CVD, increasing the likelihood of atherosclerotic events.[26] HDL-C contributes to the overall assessment of total cholesterol but is evaluated independently for its protective implications.[20]Low-Density Lipoprotein Cholesterol
Low-density lipoprotein (LDL) particles, often referred to as "bad cholesterol," serve as the primary carriers of cholesterol from the liver to peripheral tissues throughout the body.[27] These spherical lipoproteins consist of a hydrophobic core rich in cholesteryl esters and triglycerides, surrounded by a hydrophilic shell of phospholipids, free cholesterol, and one molecule of apolipoprotein B-100 (ApoB-100), which facilitates receptor-mediated uptake by cells.[28] While essential for delivering cholesterol needed for cell membrane synthesis and hormone production, LDL particles are atherogenic due to their tendency to infiltrate the arterial intima, where they can undergo oxidative modification.[29] Oxidation of LDL, triggered by reactive oxygen species in the vascular wall, transforms these particles into pro-inflammatory forms that promote endothelial dysfunction, monocyte recruitment, and foam cell formation, key steps in atherosclerotic plaque development.[30] Oxidized LDL (ox-LDL) is particularly damaging because it is recognized by scavenger receptors on macrophages, leading to unchecked uptake and lipid-laden cells that contribute to plaque buildup and arterial narrowing.[29] This process underlies the causal link between elevated LDL levels and increased risk of atherosclerotic cardiovascular disease (ASCVD).[27] In clinical practice, LDL cholesterol (LDL-C) is typically estimated indirectly using equations based on total cholesterol, HDL-C, and triglyceride levels, but this approach is unreliable when triglycerides exceed 400 mg/dL, as it overestimates or underestimates LDL-C in such cases.[31] Direct homogeneous assays, which involve enzymatic reactions to selectively measure LDL particles, offer greater accuracy in hypertriglyceridemic patients by avoiding interference from other lipoproteins.[32] These methods, though more costly, are recommended when calculated values are suspect to ensure precise risk assessment.[33] According to guidelines from the American Heart Association (AHA) and American College of Cardiology (ACC), optimal LDL-C levels for adults without ASCVD are below 100 mg/dL, with even lower targets (e.g., <70 mg/dL) for those at high risk to mitigate atherosclerosis progression.[34] Elevated LDL-C concentrations directly correlate with the extent of coronary atherosclerosis, as demonstrated in imaging and epidemiological studies, emphasizing the need for aggressive lowering in prevention strategies.[27] LDL-C constitutes the majority of total cholesterol in most individuals.[25]Triglycerides
Triglycerides are chemical compounds consisting of a glycerol molecule esterified with three fatty acid chains, forming the primary form of fat storage in adipose tissue and the main lipid component of dietary fats.[14] These molecules serve as an efficient energy reserve, releasing fatty acids when needed for metabolism, and are transported in the bloodstream primarily within lipoproteins.[35] In lipid profile testing, triglycerides are quantified through an enzymatic assay that begins with hydrolysis by microbial lipase to liberate glycerol and free fatty acids from the serum sample.[36] The freed glycerol then undergoes sequential reactions catalyzed by glycerokinase, glycerophosphate oxidase, and peroxidase, producing a colored quinoneimine dye whose absorbance is measured spectrophotometrically at 500 nm, with intensity proportional to triglyceride concentration.[36] This method ensures high specificity by including a blanking step to account for endogenous glycerol in the sample.[36] Elevated fasting triglyceride levels exceeding 150 mg/dL constitute one of the diagnostic criteria for metabolic syndrome, a cluster of conditions increasing the risk of cardiovascular disease, diabetes, and stroke.[37] Extremely high levels above 1000 mg/dL, known as severe hypertriglyceridemia, significantly elevate the risk of acute pancreatitis, potentially leading to life-threatening inflammation of the pancreas.[38] Triglycerides form the predominant lipid in very low-density lipoproteins (VLDL), facilitating their transport from the liver to peripheral tissues.[39]Very Low-Density Lipoprotein
Very low-density lipoprotein (VLDL) is a large, triglyceride-rich lipoprotein particle synthesized primarily in the liver, consisting of approximately 90% lipids and 10% proteins by composition.[40] Its lipid core is dominated by triglycerides (about 70%), with smaller amounts of cholesterol esters and free fatty acids, while the surface includes phospholipids and apolipoproteins such as apo B-100 (the structural protein), apo C-I, C-II, C-III, and apo E.[40] With a density range of 0.96–1.006 g/mL, VLDL particles are less dense than other lipoproteins due to their high triglyceride content.[40] Hepatocytes assemble VLDL particles using apo B-100 as the scaffold, facilitated by microsomal triglyceride transfer protein (MTTP), which loads triglycerides and cholesterol esters onto the nascent particle.[40] Once secreted into the bloodstream, VLDL matures by acquiring additional apolipoproteins (C-II and E) from high-density lipoprotein (HDL).[40] VLDL serves as the primary vehicle for transporting endogenous triglycerides synthesized in the liver to peripheral tissues, including adipose, cardiac, and skeletal muscle, where apo C-II activates lipoprotein lipase (LPL) to hydrolyze triglycerides and release free fatty acids for energy or storage.[40] As VLDL circulates, it progressively loses triglycerides through LPL action, transforming into intermediate-density lipoprotein (IDL); approximately half of IDL is cleared by the liver, while the remainder is further processed by hepatic lipase to remove apo E and additional lipids, ultimately converting to low-density lipoprotein (LDL).[40] VLDL is not routinely measured directly in clinical lipid profiles due to the technical challenges of ultracentrifugation; instead, it is estimated indirectly as one-fifth of the fasting triglyceride concentration in mg/dL (VLDL cholesterol ≈ triglycerides/5), an approximation valid primarily when triglycerides are below 400 mg/dL.[40] This estimation assumes a fixed ratio of triglycerides to cholesterol in VLDL particles, though it becomes less accurate in hypertriglyceridemic states.[41] Elevated VLDL levels are closely associated with insulin resistance, a condition that impairs hepatic insulin signaling and increases free fatty acid flux to the liver, thereby boosting VLDL-triglyceride secretion by 3–5 times compared to insulin-sensitive states.[42] This overproduction contributes to hypertriglyceridemia and hepatic steatosis, hallmarks of metabolic syndrome.[42] Furthermore, high VLDL promotes the formation of small, dense LDL particles through lipid exchange with HDL, enhancing their atherogenic potential by increasing arterial retention and oxidative susceptibility, thus elevating cardiovascular disease risk.[43]Testing Procedures
Indications
A lipid profile test is recommended for routine screening in adults aged 20 years and older every 4 to 6 years to assess cardiovascular risk, with more frequent testing for individuals at higher risk, such as those with a family history of premature cardiovascular disease (CVD), diabetes, hypertension, obesity, or smoking.[12] The 2018 American College of Cardiology/American Heart Association (ACC/AHA) guideline emphasizes this approach to identify dyslipidemia early, particularly in adults aged 40 to 75 years where 10-year atherosclerotic CVD (ASCVD) risk assessment guides further evaluation and management.[12] For high-risk groups, such as those with familial hypercholesterolemia or existing CVD, testing may be performed annually or as clinically indicated to monitor progression and response to interventions.[44] Specific indications for a lipid profile include the presence of symptoms suggestive of dyslipidemia, such as xanthomas (yellowish cholesterol deposits on the skin), xanthelasmas (around the eyelids), or corneal arcus in younger individuals, which warrant immediate testing to diagnose underlying lipid disorders.[45] Monitoring statin or other lipid-lowering therapy is another key indication, with the ACC/AHA guideline recommending repeat profiles 4 to 12 weeks after initiating or intensifying treatment, and periodically thereafter to evaluate efficacy and adherence.[12] In pregnancy, lipid profile testing is indicated for women with pre-existing dyslipidemia or additional CVD risk factors, as physiologic changes can exacerbate hyperlipidemia, though routine screening is not advised for all pregnant individuals.[46] Post-menopausal women, who experience hormonal shifts increasing CVD risk, should undergo testing as part of enhanced adult screening protocols, often with greater frequency if other risk factors are present.[12] For pediatric populations, universal lipid screening is recommended once between ages 9 and 11 years using a non-fasting non-HDL cholesterol measurement, with repeat screening between 17 and 21 years to detect early dyslipidemia.[47] The American Academy of Pediatrics (AAP) guidelines advise earlier and more frequent testing for children with a family history of premature CVD or hypercholesterolemia, starting as young as 2 years in high-risk cases, to enable timely intervention and prevent long-term atherosclerotic complications.[47]Sample Collection
Sample collection for a lipid profile typically involves a venous blood draw, with specific preparation guidelines to ensure accurate results. Traditionally, patients are advised to fast for 9 to 12 hours prior to the test, consuming only water, to minimize postprandial effects on triglyceride levels and allow for reliable calculation of other lipid components.[1] However, according to the 2016 European Atherosclerosis Society (EAS) consensus, non-fasting samples are acceptable and recommended for initial screening in most routine cases, as they improve patient compliance without significantly compromising cardiovascular risk assessment.[48] Fasting remains necessary for precise evaluation in patients with suspected or confirmed hypertriglyceridemia, particularly if non-fasting triglycerides exceed 5 mmol/L (approximately 443 mg/dL), to avoid underestimation of low-density lipoprotein cholesterol.[48] The procedure begins with venipuncture from a vein in the arm, using a standard needle to collect blood into a serum separator tube, such as a red-top or gold-top tube containing a clot activator.[49] The tube is gently inverted several times immediately after collection to ensure proper mixing, and the sample is then centrifuged within 45 minutes to separate serum from cellular components, preventing hemolysis or lipemia that could interfere with analysis.[49] Plasma may be used as an alternative if anticoagulants like heparin are added, but serum is preferred for most lipid assays due to its stability.[50] Patients should receive pre-test instructions to optimize result reliability, including avoiding alcohol consumption for at least 24 hours beforehand, as it can transiently elevate triglycerides and alter lipid profiles.[51] Additionally, lipid levels exhibit diurnal variation, with triglycerides typically higher in the evening due to cumulative dietary intake throughout the day, underscoring the preference for morning collections when possible.80016-3/pdf) These steps align with clinical indications for testing, such as routine cardiovascular risk screening in adults over 20 years.[1]Analytical Methods
Friedewald Equation
The Friedewald equation is a widely used method for estimating low-density lipoprotein cholesterol (LDL-C) levels from a standard lipid panel, avoiding the need for direct measurement via ultracentrifugation. Developed in 1972 by William T. Friedewald, Robert I. Levy, and Donald S. Fredrickson, it provides a practical approach for clinical assessment of cardiovascular risk based on plasma lipid concentrations.[52] The formula is expressed as: where all values are in mg/dL. This calculation assumes that very low-density lipoprotein (VLDL) cholesterol constitutes approximately 20% of triglyceride levels, hence the division by 5 to estimate VLDL-C, which is subtracted from non-HDL cholesterol to isolate LDL-C.[52] Despite its simplicity and broad adoption, the Friedewald equation has notable limitations that can affect its accuracy. It becomes unreliable when triglyceride levels exceed 400 mg/dL, as the fixed ratio assumption fails under such hypertriglyceridemia. Additionally, it is inaccurate in type III hyperlipoproteinemia due to abnormal lipoprotein compositions that invalidate the VLDL estimation. The equation also tends to underestimate LDL-C in patients with low LDL-C levels, particularly below 100 mg/dL, leading to potential misclassification of risk in certain populations.[53][54][55]Martin-Hopkins Method
The Martin-Hopkins method represents an advancement in estimating low-density lipoprotein cholesterol (LDL-C) from standard lipid panel measurements, addressing limitations of earlier calculations by using a dynamic adjustment for variability in lipoprotein composition. Developed to improve precision in diverse patient populations, it replaces the fixed division factor in prior equations with one tailored to individual lipid profiles. This approach enhances reliability for cardiovascular risk assessment, particularly in scenarios where traditional methods falter, such as elevated triglycerides or low LDL-C levels. The core formula for the Martin-Hopkins method is: The variable factor, which estimates the triglyceride-to-very low-density lipoprotein cholesterol (VLDL-C) ratio, is derived from a lookup table stratified by triglyceride levels (typically in ranges from <100 mg/dL to 300–399 mg/dL) and non-HDL cholesterol concentrations (from <100 mg/dL to >220 mg/dL), yielding values generally between 3 and 11 to better reflect empirical ratios observed in large datasets. This adjustability allows for more personalized estimation compared to fixed-ratio approaches. The method originated from a 2013 validation study analyzing over 1.1 million patients' lipid profiles against directly measured LDL-C via ultracentrifugation, revealing 10–20% greater accuracy across broader triglyceride ranges (up to 400 mg/dL) and improved classification into guideline-based risk categories, with the novel equation correctly categorizing LDL-C in 91.3% of cases versus 85.7% for the Friedewald equation. An extended version, validated in subsequent research, applies similar adjustable factors for triglycerides up to 800 mg/dL, achieving up to 62% accuracy in hypertriglyceridemic samples where other methods drop below 20%. These improvements stem from accounting for the non-constant triglyceride-VLDL-C ratio, which varies with metabolic conditions. Key advantages include robust performance with non-fasting samples, reducing logistical burdens for patients, and applicability in routine panels without specialized assays. The 2018 AHA/ACC guidelines endorse the Martin-Hopkins method over the Friedewald equation for LDL-C estimation, particularly when triglycerides exceed 150 mg/dL or LDL-C is below 70 mg/dL, to support more precise statin therapy decisions and atherosclerotic cardiovascular disease risk evaluation.Sampson-NIH Equation
The Sampson-NIH equation is a 2020 advancement for estimating low-density lipoprotein cholesterol (LDL-C) from standard lipid panels, designed for improved accuracy in patients with triglyceride levels up to 800 mg/dL. Developed by researchers at the National Institutes of Health, it incorporates adjustments for non-HDL cholesterol and triglycerides to better account for VLDL variability, validated against beta-quantification (ultracentrifugation reference).[56] The formula is: where all values are in mg/dL. This equation outperforms the Friedewald in low LDL-C scenarios and hypertriglyceridemia, with studies showing higher concordance (e.g., 89-92% accurate classification) compared to direct assays in diverse populations, including non-fasting samples. Validated in datasets exceeding 30,000 patients, it demonstrates mean absolute differences under 10 mg/dL versus reference methods, reducing misclassification risk by 15-25% over Friedewald. As of 2023, literature (e.g., Clinical Chemistry) recommends it as a preferred alternative to Martin-Hopkins for certain profiles, such as diabetes or metabolic syndrome, aligning with ongoing guideline evolutions for precise risk assessment.[57]Direct LDL Measurement
Direct measurement of low-density lipoprotein cholesterol (LDL-C) involves laboratory techniques that quantify LDL particles without relying on indirect calculations from other lipid fractions. These methods are particularly valuable in scenarios where estimation formulas, such as those detailed in other analytical approaches, become unreliable, like when triglyceride levels exceed 400 mg/dL.[58] The primary direct methods include ultracentrifugation, considered the gold standard for its precision in separating lipoprotein classes, and homogeneous enzymatic assays, which are more commonly used in clinical settings due to automation.[58] Ultracentrifugation employs density gradient separation to isolate LDL, followed by cholesterol quantification, providing high accuracy by distinguishing LDL from intermediate-density lipoprotein (IDL) and lipoprotein(a).[58] Homogeneous enzymatic assays represent the most widely adopted direct approach for routine testing. These assays use detergents and enzymes to block interference from high-density lipoprotein (HDL) and very low-density lipoprotein (VLDL), allowing selective enzymatic reaction with LDL cholesterol.[58] Developed in the 1990s and refined for autoanalyzers, examples include the Kyowa Medex and Denka Seiken methods, which offer rapid results without extensive sample preparation.[59] However, they can exhibit biases of up to 13-46% in patients with dyslipidemias due to variable lipoprotein compositions.[58] In terms of accuracy, direct methods generally align with ultracentrifugation reference procedures within a total error of 12% or less for non-diseased individuals, with biases ranging from -6.8% to 1.1% and coefficients of variation under 4%.[59] For diseased populations, performance may degrade, with total errors up to 31.9%, highlighting the need for method validation in specific clinical contexts.[59] Applications extend to research settings for detailed lipoprotein profiling and clinical cases requiring precise LDL-C values, such as hypertriglyceridemia or non-fasting samples.[58] Direct assays are 2-3 times more costly than calculated estimates due to specialized reagents and equipment, limiting their routine use but justifying them for high-stakes assessments.[60] Advanced direct techniques, such as nuclear magnetic resonance (NMR) spectroscopy, provide additional insights beyond cholesterol content by measuring LDL particle number and size distribution.[61] NMR analyzes proton signals from lipoprotein methyl groups to quantify particles, revealing small, dense LDL subtypes associated with elevated cardiovascular risk.[58] This method, while not a direct cholesterol measure, complements enzymatic assays in metabolic syndrome evaluations but requires expensive infrastructure.[58]Interpretation
Reference Ranges
Reference ranges for lipid profile components provide benchmarks for assessing cardiovascular health, derived from major clinical guidelines that classify levels as optimal, borderline, or high risk based on population studies and outcomes data. These ranges are general guidelines for healthy adults and may vary by laboratory, age, sex, and individual risk factors. Higher-risk individuals may require stricter targets. It is essential to consult a healthcare provider for personalized interpretation.[62][2] Lipid profile results are commonly reported in milligrams per deciliter (mg/dL) in the United States and some other regions, while millimoles per liter (mmol/L) is standard in many other countries. Standard conversion factors from mmol/L to mg/dL are: multiply values for total cholesterol, HDL cholesterol, and LDL cholesterol by 38.67; multiply triglyceride values by 88.57. For example, 3.5 mmol/L total cholesterol equals approximately 135 mg/dL, and 1.9 mmol/L triglycerides equals approximately 168 mg/dL. These conversions align with the equivalent values provided in guidelines and elsewhere in this article.[63] For healthy adults aged 20 years and older, general desirable ranges for lipid profile components (in mg/dL) according to major health organizations are:- Total cholesterol: Less than 200 (desirable)
- Triglycerides: Less than 150 (desirable/normal)
- HDL cholesterol: 60 or higher (optimal/best); at least 40 (men) or 50 (women) to avoid low levels
- LDL cholesterol: Less than 100 (optimal for healthy individuals; lower targets like <70 for high-risk)
- VLDL cholesterol: Less than 30 (often estimated as triglycerides divided by 5)
| Component | Optimal/Desirable (mg/dL) | Borderline (mg/dL) | High Risk (mg/dL) |
|---|---|---|---|
| Total Cholesterol | <200 | 200-239 | ≥240 |
| LDL-C | <100 | 100-129 | ≥130 |
| HDL-C (Men) | ≥60 | 40-59 | <40 |
| HDL-C (Women) | ≥60 | 50-59 | <50 |
| Triglycerides | <150 | 150-199 | ≥200 |
