A 6-year-old boy develops periorbital oedema, hypertension and cola-coloured urine two weeks after treated impetigo. Complement C3 is low. The ASO titre is within normal limits. Which test would most likely be positive?

• A Anti-DNase B titre ✓
• B Streptozyme screen for anti-M antibody
• C Throat culture for beta-haemolytic colonies
• D Anti-streptolysin O alone repeated weekly

Explanation

Streptolysin O is inhibited by skin lipids, so ASO titres rise poorly after streptococcal pyoderma. Anti-DNase B is the antibody of choice for detecting preceding skin infection with group A Streptococcus and is elevated in most cases of post-streptococcal glomerulonephritis following impetigo. Throat cultures are usually negative by the time nephritis appears because the primary lesion was cutaneous. Low C3 supports an immune-complex glomerulonephritis.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.