Dengue NS1 antigen detection is most useful diagnostically in which phase of the illness?
- A Day 6–10 (critical phase)
- B Day 10–14 (recovery phase)
- C First 5 days (febrile phase) before antibodies appear ✓
- D Equally useful throughout the illness
Correct answer: C. First 5 days (febrile phase) before antibodies appear
Explanation
NS1 antigen is detectable in blood during the viraemic/febrile phase (days 1–5) and declines once IgM antibodies appear. It is particularly useful as an early diagnostic marker when IgM/IgG antibodies may not yet be present. After day 5, NS1 sensitivity decreases while IgM ELISA becomes positive. For secondary dengue infections, NS1 may be lower due to immune complexes, making IgG avidity/IgM essential. The combination of NS1+IgM+IgG provides maximal sensitivity across all stages.
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.