IgA nephropathy vs Poststreptococcal GN
How to tell IgA nephropathy and Poststreptococcal GN apart when a board question makes them look alike.
IgA nephropathy: hematuria during the infection with normal C3; PSGN: hematuria 1 to 3 weeks after infection with low C3.
Side by side
Gross hematuria during or within days of an upper respiratory infection.
Nephritic syndrome one to three weeks after strep infection with low complement.
IgA immune complexes deposit in the mesangium.
Postinfectious immune complex deposition activates complement.
Normal complement and synpharyngitic hematuria support IgA nephropathy.
Low C3 and delayed timing support poststreptococcal GN.
The trap
Both can follow a sore throat, so the timing relative to the infection is the deciding clue. Hematuria during or within 5 days of the URI is synpharyngitic IgA nephropathy with normal C3. Hematuria 1 to 3 weeks after pharyngitis or impetigo is post-strep GN with LOW C3. Complement levels finalize: normal C3 with mesangial IgA on biopsy equals IgA; low C3 with subepithelial humps and a positive streptococcal antibody serology (ASO or anti-DNase B) equals PSGN.
Watch it explained
The repair move
Use timing and complement together: synpharyngitic/normal C3 means IgA, delayed/low C3 means PSGN.
Try a free question
CoreA patient develops gross hematuria two days after URI symptoms begin. Complement level is normal. Which diagnosis is most likely?
Show answer and explanation
Answer: A. IgA nephropathy. Synpharyngitic hematuria with normal complement points to IgA nephropathy.
Why the other choices are tempting
- B. PSGN appears after a delay and usually has low C3.
- C. Goodpasture causes pulmonary-renal disease with anti-GBM antibodies.
- D. Minimal change disease causes nephrotic syndrome.
- E. Membranous nephropathy causes nephrotic syndrome in adults.
Flashcards
Tap a card to flip it.
What timing clue favors IgA nephropathy after a URI?
Hematuria that appears during the infection or within a few days is synpharyngitic and points to IgA.
What complement pattern favors poststreptococcal GN?
Low C3 after a delayed nephritic presentation supports postinfectious complement activation.
Quick answers
What is the fastest way to tell IgA nephropathy from Poststreptococcal GN?
IgA nephropathy: hematuria during the infection with normal C3; PSGN: hematuria 1 to 3 weeks after infection with low C3.
What is the key clue for IgA nephropathy?
Gross hematuria during or within days of an upper respiratory infection.
What is the key clue for Poststreptococcal GN?
Nephritic syndrome one to three weeks after strep infection with low complement.
What is the common trap with IgA nephropathy vs Poststreptococcal GN?
Both can follow a sore throat, so the timing relative to the infection is the deciding clue. Hematuria during or within 5 days of the URI is synpharyngitic IgA nephropathy with normal C3. Hematuria 1 to 3 weeks after pharyngitis or impetigo is post-strep GN with LOW C3. Complement levels finalize: normal C3 with mesangial IgA on biopsy equals IgA; low C3 with subepithelial humps and a positive streptococcal antibody serology (ASO or anti-DNase B) equals PSGN.