Post-Streptococcal Glomerulonephritis Diagnosis and Biopsy Indications
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Direct answer
Post-streptococcal glomerulonephritis is an immune-complex nephritis that follows a nephritogenic group A streptococcal infection of the throat or skin, after a latent period of one to three weeks or three to six weeks respectively. It presents as acute nephritic syndrome with haematuria, oedema, hypertension and reduced urine output, and serum C3 is low, returning to normal within about eight weeks. Most children recover completely with supportive care, while biopsy is reserved for atypical or persistent cases.
What you must remember
- Latent period: about one to three weeks after pharyngitis and three to six weeks after impetigo or skin sepsis, the commoner trigger in tropical settings.
- Nephritic features: cola-coloured or smoky urine, periorbital oedema, hypertension and oliguria, with red-cell casts on urine microscopy.
- Low C3: complement is consumed through the alternative pathway; C3 usually normalises within about eight weeks, while C4 stays normal, which separates it from lupus nephritis.
- Antibody tests: a raised anti-streptolysin O titre follows pharyngeal infection, while anti-DNase B is more useful after skin infection.
- Biopsy pattern: diffuse endocapillary proliferation with neutrophils, and subepithelial humps on electron microscopy.
- Management: salt and fluid restriction, diuretics and antihypertensives; antibiotics treat any active infection but do not alter established glomerular injury.
- Prognosis: excellent in children; adults more often have persistent haematuria or proteinuria, and low C3 beyond eight weeks should prompt a search for other causes.
A 9-year-old with puffy eyes and cola urine
Consider a 9-year-old boy who had a sore throat three weeks ago and now has puffy eyes, cola-coloured urine and a blood pressure of 150/95 mmHg.
- Link the latent period: A sore throat three weeks earlier fits streptococcal disease, and a raised anti-streptolysin O titre would support the diagnosis.
- Read the findings: His creatinine is mildly raised, urine shows red-cell casts, and complement testing shows a low C3 with a normal C4.
- Start supportive care: Salt and fluid intake are restricted, diuretics are given for oedema, and antihypertensive therapy controls the blood pressure. Antibiotics treat any active infection but do not alter established glomerular injury.
- Monitor closely: Daily weights, blood pressure, urine output and creatinine are followed, and the team watches for hypertensive encephalopathy and pulmonary oedema.
- Decide on biopsy: A kidney biopsy is not routinely needed when the picture is typical and the C3 is recovering. It would be considered for nephrotic-range proteinuria, crescents, worsening renal impairment, or a C3 that stays low beyond about eight weeks.
Where the examiner tries to catch you
Complement results and look-alike diseases drive most questions.
- Trap: Calling any low C3 post-streptococcal. Correct: A low C3 with a normal C4 suggests post-streptococcal disease or C3 glomerulopathy, while a low C3 with a low C4 suggests lupus nephritis.
- Trap: Relying on the ASO titre after skin infection. Correct: The ASO titre is often normal after skin infection, so anti-DNase B is the better marker there.
- Trap: Missing IgA nephropathy with synpharyngitic haematuria. Correct: It is a close mimic in which gross haematuria appears within one to three days of an upper respiratory infection, with normal C3.
- Trap: Labelling any adult with nephrotic-range proteinuria as classic. Correct: Adult disease is more likely to persist, so a 40-year-old with nephrotic-range proteinuria and low C3 should not be called classic post-streptococcal disease.
Frequently asked questions
Which complement pattern distinguishes post-streptococcal glomerulonephritis from lupus nephritis?
Post-streptococcal glomerulonephritis typically shows a low C3 with normal C4, whereas lupus nephritis usually shows low C3 and low C4 together. This pattern, combined with the clinical context and antibody testing, is the basis for separating the two conditions in practice.
What is the latent period after streptococcal infection in post-streptococcal glomerulonephritis?
The latent period after streptococcal infection in post-streptococcal glomerulonephritis is about one to three weeks after pharyngitis and three to six weeks after impetigo or skin infection. The delay is important because the nephritis appears after the infection has been treated or has resolved.
When is a kidney biopsy indicated in suspected post-streptococcal glomerulonephritis?
A kidney biopsy is indicated in suspected post-streptococcal glomerulonephritis when the presentation is atypical, when nephrotic-range proteinuria or crescents are present, when renal function worsens, or when the C3 has not recovered after about eight weeks. In classic cases with recovery, biopsy is usually unnecessary.
Which serological test supports recent streptococcal infection in post-streptococcal glomerulonephritis?
Anti-streptolysin O titre and anti-DNase B are the serological tests that support recent streptococcal infection in post-streptococcal glomerulonephritis. The anti-streptolysin O titre is raised mainly after pharyngitis, while anti-DNase B is more reliable after skin infection, so both may be sent together.
What is the prognosis of post-streptococcal glomerulonephritis in adults?
Post-streptococcal glomerulonephritis has an excellent prognosis in children, with most making a full recovery, but adults are more likely to have persistent haematuria, proteinuria or reduced renal function. Adults with persistent low complement or nephrotic-range proteinuria should be evaluated for other glomerular diseases.