A 6-year-old boy develops periorbital puffiness and cola-coloured urine two weeks after crusted impetiginous lesions on his legs. Culture grew beta-haemolytic streptococci. His ASO titre is reported as normal. Which single test would be the better evidence of preceding streptococcal skin infection?

• A Antistreptokinase titre
• B Repeat ASO titre after four weeks
• C Throat swab culture for group A streptococcus
• D Anti-DNase B titre ✓

Explanation

After streptococcal skin infection, streptolysin O released into tissues is bound and neutralised by skin lipids, so the ASO response is blunted even when nephritogenic strains caused post-streptococcal glomerulonephritis. Anti-DNase B rises reliably after both skin and throat infections and is the preferred serological marker here. Repeating the ASO or culturing the throat would not document the skin infection.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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