Dengue testing is timing-dependent. From day 1 to day 5 of fever, use NS1 antigen. From day 5 onward, use IgM antibody (ELISA preferred over rapid card). IgG is most useful for distinguishing primary from secondary infection - the latter carries a higher risk of severe disease. In all dengue suspects, repeat a CBC with platelet count daily from day 3 to day 7. The critical phase is days 4-6. Falling platelets, rising haematocrit and any warning sign warrants admission.
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The three dengue tests, briefly
The dengue virus is a small RNA virus, and the three test types each pick up a different part of the infection at a different point in time:
- NS1 antigen - directly detects a viral protein in your blood. Becomes positive on day 1 of fever and remains positive through about day 5-7. After that it disappears.
- IgM antibody - the body's first immune response. Appears around day 4-5, peaks at week 2, and slowly disappears over 2-3 months. A positive IgM points to current or very recent dengue.
- IgG antibody - the longer-term immune memory. Appears later, lasts for life, and rises rapidly in secondary dengue (a second infection with a different serotype).
Rapid card tests for NS1 and IgM/IgG exist and are convenient but less sensitive than ELISA. For a definitive answer, especially when planning treatment, ELISA is preferred. At Optima Diagnostics we routinely run dengue ELISA on a same-day turnaround for our clinical partners.
Why timing is everything
This is the single most common mistake we see: a patient with fever for six days has an NS1 test, it comes back negative, and they are reassured that dengue is ruled out. NS1 simply does not last that long. By day 6, the virus has been cleared from the blood; if you want to confirm dengue at that point, you need IgM, not NS1.
The reverse mistake also happens. A patient on the second day of fever has only IgM tested - it is negative, and dengue is again incorrectly "ruled out." The IgM antibody response simply has not had time to develop yet.
Reading your result
Here are the common combinations and what they usually mean:
- NS1 positive, IgM/IgG negative (early fever) - acute dengue, very likely a first infection. Begin daily CBC monitoring.
- NS1 negative, IgM positive, IgG negative (day 5-10) - recent acute dengue, primary infection.
- NS1 negative, IgM positive, IgG positive - secondary dengue infection. Higher risk of plasma leak; monitor more carefully.
- NS1 negative, IgM negative, IgG positive - past dengue infection at some point. Does not imply current illness.
- All negative - dengue is unlikely if the sample timing matches, but consider repeating after 24-48 hours if clinical suspicion is strong. Consider scrub typhus, leptospirosis, malaria, COVID-19 and seasonal viral illnesses, which all overlap with dengue in our region.
CBC and platelets - the real monitoring
Confirming dengue is the start, not the end. The real work of dengue management is tracking the complete blood count daily through the critical window. We watch three things:
- Platelet count. Often falls from a normal 1.5-4 lakh/µL to 50,000-1 lakh in uncomplicated dengue. The absolute number matters less than the trend. A platelet of 60,000 that is rising is good news; a platelet of 90,000 that is falling rapidly is not.
- Haematocrit (packed cell volume). Rising haematocrit signals plasma leaking out of the vessels - the hallmark of severe dengue. A 20% rise from baseline is a red flag.
- White cell count. Typically low (leucopaenia) in dengue. A relative rise of lymphocytes is often the first sign of recovery.
Most uncomplicated dengue is managed at home with adequate oral fluids, paracetamol for fever, and daily monitoring. Do not use aspirin, ibuprofen or other NSAIDs - they worsen bleeding risk. Salicylates in particular are best avoided in any acute fever in our region until dengue and scrub typhus have been excluded.
Warning signs you must not ignore
The WHO 2009 guidelines list specific warning signs that mandate hospital admission, regardless of platelet count:
- Severe abdominal pain or tenderness
- Persistent vomiting (more than 3 times in an hour)
- Mucosal bleeding (gums, nose, blood in urine or stools)
- Lethargy, restlessness, irritability or confusion
- Liver enlargement on examination
- Rising haematocrit with a falling platelet count
These usually appear around defervescence - when the fever finally breaks, often on day 4 or 5. Counter-intuitively, this is the most dangerous time, not the safest.
One sentence to remember: in dengue, the day the fever stops is the day to stay alert - not the day to relax.
Myths we still hear in Silchar
"Papaya leaf juice raises platelet count." Several small studies show a modest effect on platelets, but no clinical trial has shown it changes the outcomes that matter - bleeding, length of illness, or mortality. It is not a substitute for monitoring.
"A platelet count below 1 lakh means I need a transfusion." No. Platelet transfusion in uncomplicated dengue is not indicated until counts fall below 10,000-20,000 or there is active bleeding. Transfusing more aggressively does not help and may harm.
"If I had dengue before, I cannot get it again." Wrong - and dangerously so. There are four dengue serotypes. Infection with one gives long-term immunity to that strain only. Catching a different serotype later (secondary infection) carries a higher risk of severe disease.
Dengue testing in Silchar
At Optima Diagnostics, we offer NS1 antigen (rapid and ELISA), IgM/IgG ELISA, and same-day CBC with platelet count. We are open seven days a week through the monsoon season, when dengue cases in Cachar typically peak. During outbreaks we extend hours and prioritise platelet counts so worried families do not wait long for the morning result. Home collection is available for unwell patients - the same technician who draws today comes back tomorrow for the follow-up sample, so platelet trends are reliable.
Frequently asked questions
Which dengue test on day 1 of fever?
NS1 antigen. It is the only dengue test reliably positive from day 1 to day 5. IgM and IgG usually become positive only after day 4-5.
Can I test negative and still have dengue?
Yes. A negative NS1 after day 5, or a negative IgM in the first 3 days, does not rule out dengue. Repeat testing or order the correct test for that day of illness.
How often should the platelet count be repeated?
Daily from day 3 to day 7 in confirmed or strongly suspected dengue. The critical phase is days 4-6.
Does a low platelet count always mean severe dengue?
No. Platelets routinely drop to 50,000-100,000 in uncomplicated dengue and recover. Warning signs - bleeding, severe pain, vomiting, lethargy, rising haematocrit - matter more than the platelet number alone.
Can dengue come back?
Yes. There are four serotypes and immunity to one does not protect against the others. A secondary infection carries a higher risk of severe disease.
This article is for general education. Anyone with suspected dengue should be reviewed by a treating doctor and monitored closely.
