A 9-year-old boy develops haematuria and periorbital oedema two weeks after an episode of impetigo. Antistreptolysin O titre is normal. Which additional antibody test would best support recent streptococcal infection?

• A Rheumatoid factor
• B ASO titre repeated after one week
• C Anti-M protein antibody titre
• D Anti-DNase B titre ✓

Explanation

Skin lipids inhibit streptolysin O, so ASO titres rise poorly or not at all after pyoderma-associated post-streptococcal glomerulonephritis. Anti-DNase B is the antibody of choice because it rises reliably after both pharyngeal and cutaneous streptococcal infections. Repeating ASO would remain unhelpful here. Anti-M protein antibodies are type specific and not routinely measured clinically. Rheumatoid factor has no role in confirming streptococcal infection.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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