Medically reviewed by Dr. Ponlawat Pitsuwan, Physician, Takecare Clinic Phuket. Last reviewed: September 2026.
In the rainy season I test a lot of feverish patients for dengue, and the timing of the test matters. An NS1 antigen test works best in the first few days of fever, while antibody tests become useful later, so I always ask exactly when the fever began.
Most visitors we test for dengue arrive on the first to third day of a sudden fever, often sure it is heatstroke, a hangover or something they ate. The clue is usually the combination: a high temperature that came on within hours, a headache felt behind the eyes, and aching muscles that make a bed feel like concrete. Aedes mosquitoes, the day-biting species that carry the virus, breed in plant saucers, discarded containers and building sites all over the island, and they are busiest in the rainy months from about May to October. Getting the right test on the right day saves a wasted blood draw and, more importantly, tells us when to start watching your platelets closely.
Why the day of fever decides the test
Dengue has two detection windows. Early on, the virus and a protein it sheds, called NS1 (non-structural protein 1), circulate in the blood. As the immune system responds, antibodies appear: IgM, the early antibody, and IgG, the long-lasting one. The virus markers fade as the antibodies rise, so a test that is excellent on day two may miss the infection on day seven, and the reverse is also true.
Counting days correctly matters. Day one is the day the fever started, not the day you felt worried enough to see a doctor. If you are unsure, tell us what you were doing when the first chills began and we work it out together.
| Test | What it detects | Best timing | Main limitation |
|---|---|---|---|
| NS1 antigen (rapid or lab) | A viral protein | Days 1 to 5 of fever | Less sensitive in a second dengue infection and after day 5 |
| IgM antibody | Recent immune response | From about day 5; stays positive for 2 to 3 months | Often negative early; can cross-react with Zika |
| IgG antibody | Past or repeat infection | Rises early and high in a second infection | Positive alone usually means a past infection |
| NS1/IgM/IgG combo rapid test | All three on one cassette | Any day, read in about 15 to 20 minutes | A screening test; a negative is weighed against symptoms |
| RT-PCR | Viral genetic material and serotype | Days 1 to 5 | Usually a hospital or reference laboratory test |
| Full blood count (CBC) | Platelets, white cells, haematocrit | At diagnosis, then daily from about day 3 | Does not diagnose dengue on its own |
Reading the result combinations
A positive NS1 in a feverish traveller is strong evidence of current dengue. A negative NS1 on day one or two does not rule it out, particularly if you have had dengue before, because a second infection can clear NS1 quickly. In that case we either repeat the test or add antibodies after day five, guided by how you look. A positive IgM points to an infection in the last few weeks. A positive IgG on its own, with no NS1 or IgM, usually means you had dengue at some point in the past, sometimes without knowing. Japanese encephalitis or yellow fever vaccination and Zika infection can also cause some antibody cross-reaction, which is why the doctor interprets results alongside your history rather than reading the cassette in isolation.
A strongly positive IgG early in the illness, together with a positive NS1 or IgM, suggests a second infection with a different dengue type. There are four types, and a second infection carries a higher chance of severe disease, so this pattern makes us monitor you more closely.
The blood count: the safety test
While the antibody and NS1 tests answer “is this dengue?”, the full blood count answers “how is it behaving?”. A falling white cell count, often below 5,000 per microlitre, commonly comes before the critical phase. Platelets, the cells that help blood clot, drop over several days, and a count falling towards or below 100,000 per microlitre is a threshold doctors watch. A rise in haematocrit, the proportion of blood made up of red cells, of about 20 percent above your baseline suggests fluid is leaking out of blood vessels. For this reason we usually repeat the count every 24 hours from about day three until the fever has been gone for a day or two. Liver enzymes are often mildly raised and are checked if you feel very unwell.
Some doctors also perform a tourniquet test, in which a blood pressure cuff is inflated on the arm for five minutes and small pinpoint spots below it are counted. It is a simple bedside sign that supports, but never replaces, blood tests.
What happens during your test visit
We take your temperature, pulse and blood pressure, ask which day your fever began, where you have been and whether you have had dengue before, and examine you for rash, bruising, abdominal tenderness and dehydration. A single blood sample usually covers the rapid dengue test and the blood count. While results are processed, we give paracetamol if you need it and advise you to avoid ibuprofen, aspirin and other anti-inflammatory painkillers until dengue has been ruled out, because they can worsen bleeding.
If the test is positive, the doctor explains what the next days will look like and sets up monitoring, which is covered on our dengue fever treatment page. If it is negative but you still have fever, we look for other causes. In Phuket that can mean chikungunya, influenza, a urine infection or, after muddy water or waterfall trips, leptospirosis, and a malaria test if you arrived from forested border areas. Our wider fever treatment guide describes that process.
When to see a doctor
Get tested on the first or second day of any sudden fever above 38°C in Phuket, especially with headache behind the eyes, joint or muscle pain, or a rash. If you already know you have dengue, the warning signs of severe disease need hospital care rather than another clinic test.
Prevention and early detection
Aedes mosquitoes bite mostly in daylight, with peaks in the early morning and late afternoon, so evening-only repellent is not enough. Use a repellent containing DEET at 20 to 50 percent, picaridin at about 20 percent or IR3535 on exposed skin, reapplying after swimming and applying sunscreen first. Light long sleeves help at dawn and dusk, and air-conditioned or well-screened rooms reduce night-time bites. If you are staying in a villa, tip out any standing water in pots, buckets and drains every few days.
A dengue vaccine is licensed in Thailand. It is a two-dose course given three months apart, so it cannot protect a holiday already in progress, and advice on who should have it differs between countries, with some recommending it mainly for people who have had dengue before. Ask us on WhatsApp whether it is in stock today.
Getting tested at Takecare Clinic
We are open 24 hours a day at three clinics, each with an on-site laboratory. The fastest route is to walk in: our Bangtao (Cherngtalay) clinic serves the north-west beaches, the Kata-Karon clinic covers the south-west, and the Patong clinic is close to the town centre. If you would like to check the price or describe your symptoms first, send a message on WhatsApp or call +66 81 718 9080.
Many feverish travellers would rather not leave their room, and a doctor hotel visit in Phuket means the sample is taken where you are staying and processed in our lab. Dengue testing for a fever is normally claimable on travel insurance; we offer direct billing with most travel insurers and give you receipts, a medical report and an itemised invoice.
Related services and treatments
A dengue screen is one of several blood tests in Phuket we run daily, and it is not part of a routine health check-up in Phuket, because it is only useful when you have symptoms. For any other new problem, our walk-in doctor in Phuket service is available at all hours, and the full list is under all our medical services.
Summary
The right dengue test depends on the day of your fever: NS1 in the first five days, IgM and IgG from about day five, and a full blood count throughout to follow platelets, white cells and haematocrit. A negative early result does not end the question if you still have fever, and the days when the fever falls are the ones to watch most carefully. Get tested early, take only paracetamol until dengue is ruled out, and go to hospital immediately if any warning sign appears.
“If you have a fever in Phuket, avoid ibuprofen and aspirin until dengue has been ruled out. Paracetamol is the safer choice while you wait for results.”
Dr. Ponlawat Pitsuwan, Physician, Takecare Clinic Phuket
Frequently asked questions
Will travel insurance pay for my dengue test?
A dengue test ordered by a doctor because you have a fever is a diagnostic test for a new illness, which most travel insurance policies cover, subject to their excess and terms. We offer direct billing with most travel insurers and provide receipts, an itemised invoice and a medical report for claims. We confirm the price on WhatsApp before your visit if you are paying yourself.
How quickly will I know if it is dengue?
Rapid NS1 and antibody cassettes are designed to be read within about 15 to 20 minutes of the sample reaching the laboratory, and the full blood count is processed on site as well. Most people have their dengue and blood count results the same day, usually within a few hours, and the doctor explains them straight away and plans any repeat checks.
My NS1 was negative on day one. Could I still have dengue?
Yes. NS1 is good but not perfect, and it can be missed very early, late, or in a second dengue infection. If your fever continues, we repeat the test or add IgM and IgG antibodies from about day five, and follow your blood count. Until dengue is ruled out, keep to paracetamol and avoid ibuprofen and aspirin.
Can someone test me for dengue in my hotel room?
Yes. A doctor can visit your hotel or villa anywhere in Phuket at any hour, assess you, take the blood sample and bring it back to our laboratory. This suits people with high fever who feel too weak to travel or parents with a sick child. If the doctor sees warning signs during the visit, you will be advised to go to hospital instead.
Do I need a booking or a referral for dengue testing?
No referral is needed and you can walk in at any of our three clinics day or night, where most people are seen within minutes. A doctor always sees you first, because the choice of test depends on your day of fever and symptoms. A WhatsApp message beforehand is helpful but optional.
I had dengue on a previous trip. Will the test show it, and does it matter?
A positive IgG with negative NS1 and IgM usually reflects a past infection, so the test can show it. It matters because a second infection with a different dengue type carries a higher risk of severe disease. Tell the doctor about any earlier dengue, as it changes how closely we monitor your platelets and fluids.
Sources
The World Health Organization fact sheet on dengue and severe dengue sets out the warning signs and the global picture. The CDC guidance on dengue diagnosis and testing explains when NS1, PCR and antibody tests are most accurate. MedlinePlus summarises platelet tests and what a low count means.
dengue test, dengue fever, dengue virus, NS1 antigen test, dengue IgM, dengue IgG, NS1/IgM/IgG combo rapid test, RT-PCR, full blood count, platelet count, thrombocytopenia, leukopenia, haematocrit, tourniquet test, secondary dengue infection, Aedes aegypti, Aedes albopictus, chikungunya, Zika, leptospirosis, paracetamol, DEET, picaridin, WHO, CDC, MedlinePlus, Bangtao, Cherngtalay, Kata, Karon, Patong, Takecare Clinic Phuket, Dr. Ponlawat Pitsuwan
This page is general health information and not a substitute for a medical consultation.