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Diagnosis of acute poststreptococcal glomerulonephritis
Medical expert of the article
Last reviewed: 06.07.2025
Acute poststreptococcal glomerulonephritis always manifests itself with pathological changes in the urine. Hematuria and proteinuria are always present, usually there are casts. In freshly collected urine samples, erythrocyte casts are often found, and phase-contrast microscopy can reveal dysmorphic ("altered") erythrocytes, indicating the glomerular origin of hematuria. Also, the diagnosis of acute poststreptococcal glomerulonephritis reveals tubular epithelial cells, granular and pigment casts, leukocytes. In patients with severe exudative glomerulonephritis, leukocyte casts are sometimes found. Proteinuria is a characteristic sign of acute poststreptococcal glomerulonephritis; however, nephrotic syndrome at the onset of the disease is present in only 5% of patients. Sometimes a transient increase in proteinuria is noted after 1-2 weeks of the disease as the CF rate is restored.
[ Laboratory diagnostics of acute poststreptococcal glomerulonephritis
Urine: protein, erythrocytes, casts. Glomerular filtration: initially decreased in some patients. (T serum creatinine >2 mg% in 25% of cases). Antistreptococcal antibodies:
- in patients with pharyngitis > 95%;
- in patients with skin infection - 80%;
- false positive results - 5%;
- Early antibacterial therapy suppresses the antibody response. CH50 and/or C3, C4: decrease in levels > 90%. Hypergammaglobulinemia - 90%. Polyclonal cryoglobulinemia - 75%.
Serum creatinine concentration is usually elevated (>2 mg/dL in about 25% of patients), although it remains within the upper limit of normal in some. The creatinine filtration rate is almost always decreased initially but returns to normal as the disease resolves.
In the first 2 weeks of nephritis activity, the level of C3 and CH50 is reduced in more than 90% of patients, C4 usually remains normal or sometimes slightly reduced; its marked reduction indicates the presence of another disease (mesangiocapillary glomerulonephritis, lupus nephritis, essential mixed cryoglobulinemia). The level of properdin is usually low and reflects the interest of the alternative pathway of complement activation. In most cases, complement indices return to normal by the 4th week, but sometimes this is delayed for up to 3 months. C3-nephritic factor is absent or detected in low concentrations, a high and persistent increase in its concentration is more typical of mesangiocapillary glomerulonephritis.
90% of patients have hypergammaglobulinemia, 75% have polyclonal transient cryoglobulinemia.
Antibodies to extracellular products of streptococcus: antistreptolysin-O, antihyaluronidase, antistreptokinase, antinicotinamide adenine dinucleotidase (anti-NAD) and anti-DNase B are detected in more than 95% of patients with pharyngitis and in 80% of patients with skin infection. Titers of antistreptolysin-O, anti-DNase B, anti-NAD and antihyaluronidase usually increase after pharyngitis, while anti-DNase B and antihyaluronidase - more often after skin infection. These tests for streptococcal infection are quite specific: false-positive results are no more than 5%. Since the prevalence of streptococcal infection among children is quite high, elevated titers indicate primarily the presence of streptococcal infection in patients, and not the presence of nephritis. The titers of these antibodies increase 1 week after the onset of infection, reach a peak after 1 month, and gradually return to their initial level before the disease over several months. Antibodies against M proteins are type-specific and indicate immunity to certain strains. They are detected 4 weeks after the onset of infection and persist for several years. Early treatment of acute post-streptococcal glomerulonephritis with antibiotics often interrupts the development of an antibody response to both extracellular products and M proteins of streptococcus. Therefore, negative results of a study on antistreptococcal antibodies in patients who have previously received antibiotics do not exclude a diagnosis of a previous streptococcal infection.