Hematuria

Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. "Gross hematuria" occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable with a microscope or laboratory test. Blood that enters and mixes with the urine can come from any location within the urinary system, including the kidney, ureter, urinary bladder, urethra, and in men, the prostate. Common causes of hematuria include urinary tract infection (UTI), kidney stones, viral illness, trauma, bladder cancer, and exercise. These causes are grouped into glomerular and non-glomerular causes, depending on the involvement of the glomerulus of the kidney. But not all red urine is hematuria. Other substances such as certain medications and some foods (e.g. blackberries, beets, food dyes) can cause urine to appear red. Menstruation in women may also cause the appearance of hematuria and may result in a positive urine dipstick test for hematuria. A urine dipstick test may also give an incorrect positive result for hematuria if there are other substances in the urine such as myoglobin, a protein excreted into urine during rhabdomyolysis. A positive urine dipstick test should be confirmed with microscopy, where hematuria is defined by three or more red blood cells per high power field. When hematuria is detected, a thorough history and physical examination with appropriate further evaluation (e.g. laboratory testing) can help determine the underlying cause.

Hematuria can be classified according to visibility, anatomical origin, and timing of blood during urination.

Many causes may present as either visible hematuria or microscopic hematuria, and so the differential diagnosis is frequently organized based on glomerular and non-glomerular causes.

Hematuria due to a glomerular source commonly presents as dysmorphic red blood cells (misshapen red blood cells) or red cell casts (small tubular structures made up of red blood cell components) on urine microscopy. This occurs due to the red blood cells being deformed as they pass through the glomerular capillaries into the renal tubules and eventually into the urinary system. Normally, red blood cells should never pass from the glomerular capillary into the renal tubule, and this is always a pathological process. Glomerular causes include:

Visible blood clots in the urine indicate a non-glomerular cause. Non-glomerular causes include:

Not all red or brown urine is caused by hematuria. Other substances such as certain medications and certain foods can cause urine to appear red.

Medications that may cause urine to appear red include:

Foods that may cause urine to appear red include: