Dengue NS1 vs IgM Antibody Test: Which One Do You Need?

By Dashvanth Healthcare Medical Team · Reviewed by our specialists · East Delhi

Dengue Testing: Timing Is Everything

Dengue has two distinct phases that require different tests. Using the wrong test at the wrong time gives false-negative results — leading to missed diagnoses. Understanding which test to use when is crucial.

NS1 Antigen Test

• What it detects: Dengue virus NS1 protein (directly detects the virus)
• When to use: Day 1–5 of fever (early phase)
• Sensitivity: 90% in first 3 days; falls to 40–50% by Day 5
• Positive result: Confirms dengue — start monitoring
• Negative result: Does NOT rule out dengue if tested after Day 5

IgM and IgG Antibody Tests

• What they detect: Your immune system's antibody response to dengue
• IgM: Appears Day 4–5 of illness; peaks by Day 14; indicates CURRENT or RECENT infection
• IgG: Appears later; elevated in secondary dengue (second dengue infection)
• When to use: Day 5+ of fever (after NS1 becomes less reliable)
• ELISA-based IgM is more accurate than rapid IgM tests

Practical Guide

CBC in Dengue

• Falling platelet count (thrombocytopenia) confirms dengue and guides severity
• Haematocrit rise (>20% from baseline) suggests plasma leakage (severe dengue)