Glomerular Disease
Core concepts
Glomerular disease questions reward a pattern-recognition approach: nephritic (hematuria, RBC casts, hypertension, oliguria, subnephrotic proteinuria) versus nephrotic (proteinuria >3.5 g/day, hypoalbuminemia, edema, hyperlipidemia). Then place the lesion by complement and immunofluorescence.
- Low C3: post-infectious GN (low C3, normal C4, resolves in 6–8 weeks), MPGN/C3 glomerulopathy, lupus nephritis, cryoglobulinemia.
- Normal complement: IgA nephropathy (mesangial IgA; synpharyngitic hematuria), anti-GBM disease (linear IgG, pulmonary-renal syndrome), ANCA vasculitis (pauci-immune), Henoch-Schönlein purpura.
- Nephrotic: minimal change disease (children, selective proteinuria, steroid-responsive), FSGS (HIV, APOL1, obesity, heroin), membranous nephropathy (anti-PLA2R, malignancy screen in adults), diabetic nephropathy, amyloidosis.
Traps
Questions love timing: IgA hematuria appears 1–2 days after a URI, post-infectious GN 1–3 weeks after. Anti-GBM and ANCA are both rapidly progressive GN but differ on IF (linear vs pauci-immune). Do not call membranous "steroid-responsive"; do not miss secondary causes of FSGS. In lupus nephritis, class III/IV and membranous (V) drive treatment decisions, and crescents imply aggressive therapy.
Rule of thumb
RBC casts + hypertension + low C3 = nephritic workup now; nephrotic-range proteinuria in an adult = biopsy unless diabetes with classic retinopathy and long-standing disease.
Worked example
A 24-year-old develops dark urine 2 days after pharyngitis with normal C3/C4 and mesangial IgA on biopsy. Diagnosis: IgA nephropathy; supportive care, ACE inhibitor if proteinuric; immunosuppression reserved for progressive disease.