14.2 Glomerulonephritis & Hematuria

Glomerulonephritis & Hematuria

The distinction between post-streptococcal glomerulonephritis and IgA nephropathy — by infection-to-hematuria timing and complement level — is a recurring single-best-answer theme on the Arab Board written paper, alongside structured hematuria work-up questions.

Post-Streptococcal Glomerulonephritis (PSGN)

Post-streptococcal glomerulonephritis (PSGN) is an immune-complex-mediated nephritis that follows infection with nephritogenic strains of Group A Streptococcus (Streptococcus pyogenes). Unlike minimal change disease, PSGN is a nephritic, not nephrotic, process — the primary problem is glomerular inflammation causing hematuria and reduced glomerular filtration rate, not primarily a leaky filtration barrier.

Timing is diagnostic. There is a latency period between the streptococcal infection and the onset of renal disease, reflecting the time needed for immune complexes to form and deposit in the glomeruli:

Peak incidence is between ages 5 and 12; PSGN is uncommon under age 3. Presentation follows the classic nephritic picture: gross, tea- or cola-colored hematuria, periorbital edema, hypertension from sodium and water retention, and oliguria. Proteinuria is usually present but rarely reaches nephrotic range. Severe hypertension can occasionally cause hypertensive encephalopathy, a genuine emergency.

Key labs: C3 is low because of activation of the alternative complement pathway, while C4 is usually normal. Evidence of the antecedent streptococcal infection is documented with an elevated ASO (anti-streptolysin O) titer, which is more useful after pharyngitis, or an elevated anti-DNase B titer, which is more sensitive after skin infection since the ASO response to impetigo is often blunted. A throat or skin culture is not required for diagnosis. C3 should normalize within 6-8 weeks; a persistently low C3 beyond that window should prompt referral for biopsy to rule out membranoproliferative glomerulonephritis or another chronic complement-mediated disease. Treatment is supportive — sodium and fluid restriction, diuretics, and antihypertensives as needed — and the pediatric prognosis is excellent, with the great majority of children recovering fully.

Exam trap: do not confuse the expected, self-limited course of PSGN with rapidly progressive glomerulonephritis (RPGN). If a child with an apparent nephritic illness instead shows a steadily rising creatinine over days to weeks, oliguria that fails to improve, or crescents on biopsy, think beyond routine PSGN toward a crescentic process (which can rarely complicate severe PSGN, or point to a distinct vasculitic or anti-GBM disease) and escalate the work-up accordingly rather than assuming the benign PSGN trajectory will hold.

IgA Nephropathy vs. PSGN: The Timing Distinction

IgA nephropathy (Berger disease) is the most common cause of chronic glomerulonephritis worldwide, and it is a frequent examiner favorite specifically because of how it is distinguished from PSGN: by timing relative to the preceding infection.

The distinction worth internalizing: PSGN hematuria appears weeks after the sore throat has resolved, while IgA nephropathy hematuria appears together with the sore throat. Definitive diagnosis of IgA nephropathy requires a renal biopsy showing mesangial IgA deposits, but a normal C3 with synpharyngitic timing should already move it to the top of the differential on a written exam. IgA vasculitis (Henoch-Schönlein purpura) is a related, IgA-mediated systemic small-vessel vasculitis presenting with palpable purpura over the lower extremities and buttocks, arthralgia, abdominal pain, and nephritis; its renal lesion is histologically identical to isolated IgA nephropathy.

Approach to Hematuria: Glomerular vs. Non-Glomerular

Hematuria is generally defined as more than 5 red blood cells per high-power field on microscopy. The first branch point in any hematuria question is whether the bleeding source is glomerular or non-glomerular (lower urinary tract):

For a child with isolated microscopic hematuria found incidentally, for example on a school physical, with no proteinuria, casts, or hypertension, the two most common benign explanations are idiopathic hypercalciuria, screened with a spot urine calcium:creatinine ratio, and thin basement membrane nephropathy (benign familial hematuria). Initial workup includes urinalysis with microscopy, urine culture, blood pressure, renal function testing, and C3/C4; ASO and anti-DNase B titers are added if PSGN is suspected. A family history of renal failure and deafness in male relatives should raise concern for Alport syndrome, most commonly X-linked (COL4A5), which classically presents with the triad of hematuria, sensorineural hearing loss, and ocular abnormalities such as anterior lenticonus, and can progress to end-stage renal disease.

Worked scenario: A 6-year-old girl develops tea-colored urine and facial swelling about 10 days after recovering from strep pharyngitis. Blood pressure is 130/85 mmHg, C3 is low, and ASO titer is elevated. Supportive care with salt and fluid restriction is appropriate; C3 should be rechecked in 6-8 weeks to confirm normalization.