Nephritic syndrome is a syndrome comprising signs of nephritis, which is kidney disease involving inflammation. It often occurs in the glomerulus, where it is called glomerulonephritis. Glomerulonephritis is characterized by inflammation and thinning of the glomerular basement membrane and the occurrence of small pores in the podocytes of the glomerulus. These pores become large enough to permit both proteins and red blood cells to pass into the urine (yielding proteinuria and hematuria, respectively). By contrast, nephrotic syndrome is characterized by proteinuria and a constellation of other symptoms that specifically do not include hematuria. Nephritic syndrome, like nephrotic syndrome, may involve low level of albumin in the blood due to the protein albumin moving from the blood to the urine.

Historically, nephritic syndrome has been characterized by blood in the urine (hematuria), high blood pressure (hypertension), decreased urine output <400 ml/day (oliguria), red blood cell casts, pyuria, and mild to moderate proteinuria. If the condition is allowed to progress without treatment, it can eventually lead to azotemia and uremic symptoms. This constellation of symptoms contrasts with the classical presentation of nephrotic syndrome (excessive proteinuria >3.5 g/day, low plasma albumin levels (hypoalbuminemia) <3 g/L, generalized edema, and hyperlipidemia).

Signs and symptoms that are consistent with nephritic syndrome include:

Nephritic syndrome is caused by extensive inflammatory damage to the glomerulus capillaries, which is associated with a variety of medical conditions that we will discuss. Furthermore, the cause of this inflammation can be infectious, autoimmune, or thrombotic. The causative conditions can be divided conveniently between age groups as follows, though it is important to note that many of the conditions listed in children/adolescents can also occur in adults with lower frequency, and vice versa:

The pathophysiology of nephritic syndrome is dependent on the underlying disease process, which can vary depending on what condition the nephritic syndrome is secondary to. More specifically, different diseases (many of which are mentioned above in the Causes section) affect different segments of the glomerulus and cause disease-specific segments of the glomerulus to become inflamed. Most often, it is dependent on what part of the glomerulus is damaged by antibody-antigen complex (immune complex) deposition. In all cases, however, the inflammatory processes in the glomerulus cause the capillaries to swell and the pores between podocytes become large enough that inappropriate contents in the blood plasma (i.e. red blood cells, protein, etc.) will begin to spill into the urine. This causes a decrease in glomerular filtration rate (GFR) and, if left untreated over time, will eventually produce uremic symptoms and retention of sodium and water in the body, leading to both edema and hypertension.

The diagnostic approach to nephritic syndrome includes evaluating the patient for any suspected underlying pathology that could cause a nephritic syndrome.^{[citation needed]}

If the person in the office is being examined by a physician, some physical exam findings consistent with nephritic syndrome include the following:

If the physician is suspicious of a possible nephritic syndrome, then he/she may order some common lab tests including: