Rheumatic fever vs Post-strep glomerulonephritis
How to tell Rheumatic fever and Post-strep glomerulonephritis apart when a board question makes them look alike.
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Low serum C3 with nephritic urine sediment is the fast discriminator for post-streptococcal glomerulonephritis.
Side by side
Migratory polyarthritis, carditis, chorea, or erythema marginatum after untreated streptococcal pharyngitis suggests acute rheumatic fever.
Tea-colored urine, edema, hypertension, and low complement after streptococcal infection suggest post-streptococcal glomerulonephritis.
Molecular mimicry after group A streptococcal pharyngitis causes autoimmune inflammation in joints, heart, skin, and CNS.
Immune-complex deposition in glomeruli after streptococcal infection causes complement consumption and nephritic syndrome.
Evidence of recent streptococcal infection plus Jones criteria, with elevated ESR or CRP and often prolonged PR interval; complement C3 is typically normal.
Urinalysis shows hematuria with RBC casts and mild to moderate proteinuria, C3 is low in the acute phase, and ASO or anti-DNase B titers are elevated.
The trap
Both conditions follow streptococcal infection, so clinicians may overcall rheumatic fever when edema and cola urine are present; nephritic findings and hypocomplementemia redirect diagnosis toward glomerulonephritis.
The repair move
Next best step: if nephritic syndrome with low C3 is present, manage post-streptococcal glomerulonephritis supportively with salt restriction, loop diuretic such as furosemide 1 mg/kg IV or PO, and blood-pressure control while monitoring renal function; treat active streptococcal infection with penicillin if still present. If Jones criteria support rheumatic fever, give penicillin to eradicate GAS and start anti-inflammatory therapy such as high-dose aspirin 80 to 100 mg/kg/day divided every 6 hours, then begin long-term benzathine penicillin prophylaxis every 4 weeks.
Try a free question
CoreA 9-year-old girl has facial puffiness and dark urine 2 weeks after streptococcal skin infection. BP 146/92 mm Hg, HR 104/min, temp 36.9 C. Urinalysis shows RBC casts and C3 is low. What is the next best step in management?
Show answer and explanation
Answer: A. Begin salt restriction and furosemide with blood-pressure monitoring. Low C3 nephritic syndrome after strep infection is PSGN, managed primarily with supportive volume and blood-pressure control.
Why the other choices are tempting
- B. Wrong because secondary prophylaxis is a rheumatic fever strategy, not PSGN standard care.
- C. Wrong because aspirin is for inflammatory manifestations of rheumatic fever.
- D. Wrong because immunosuppression is not routine in typical PSGN.
- E. Wrong because children still need close follow-up for BP and renal recovery.
Flashcards
Tap a card to flip it.
After recent streptococcal illness, which lab finding points toward post-streptococcal glomerulonephritis rather than rheumatic fever?
Low complement C3 with hematuria and RBC casts points to post-streptococcal glomerulonephritis.
Which syndrome is defined by Jones criteria rather than nephritic urine findings?
Acute rheumatic fever is diagnosed by Jones criteria plus evidence of recent GAS infection.
Quick answers
What is the fastest way to tell Rheumatic fever from Post-strep glomerulonephritis?
Low serum C3 with nephritic urine sediment is the fast discriminator for post-streptococcal glomerulonephritis.
What is the key clue for Rheumatic fever?
Migratory polyarthritis, carditis, chorea, or erythema marginatum after untreated streptococcal pharyngitis suggests acute rheumatic fever.
What is the key clue for Post-strep glomerulonephritis?
Tea-colored urine, edema, hypertension, and low complement after streptococcal infection suggest post-streptococcal glomerulonephritis.
What is the common trap with Rheumatic fever vs Post-strep glomerulonephritis?
Both conditions follow streptococcal infection, so clinicians may overcall rheumatic fever when edema and cola urine are present; nephritic findings and hypocomplementemia redirect diagnosis toward glomerulonephritis.