In Dengue, the 'NS1 antigen test' detects non-structural protein 1, which is secreted abundantly during early dengue infection. In a patient presenting on Day 5 of fever with platelet count 85,000/µL, which combination of diagnostic tests has the HIGHEST combined sensitivity?

• A NS1 antigen test alone
• B NS1 antigen + IgM ELISA ✓
• C IgG avidity test to distinguish primary from secondary infection
• D Dengue PCR alone — most sensitive on Day 5

Explanation

NS1 antigen is maximally detectable in blood during Days 1–5 of acute infection and declines thereafter. IgM antibodies rise from Day 3–5 and peak around Days 10–14. By Day 5, NS1 sensitivity begins to decline while IgM starts to rise. The combination of NS1 antigen ELISA + IgM ELISA provides the highest combined sensitivity (>90%) at this transitional window (Day 4–5). PCR is most sensitive in the first 3–4 days and also declines by Day 5. IgG avidity helps classify primary vs secondary infection but does not improve diagnostic sensitivity for current infection.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.