A dengue test is usually requested after a few days of high fever, often with a severe headache and pain behind the eyes. Which test is useful depends on how long you have been ill, because each one picks up the infection at a different stage.
Which test to ask for on which day
Start counting from the first day of fever. In the first seven days, the usual request is an NS1 antigen test together with a dengue IgM antibody test. A PCR test, which looks for the virus's genetic material, works in the same early window and can take the place of NS1 in that pairing.
After day seven, NS1 and PCR are less reliable. IgM becomes the main test at that point; it starts picking up most infections once you are past the third day of illness.
Going to a lab with a doctor's slip? Tell the counter staff which day of fever you are on, so they can check the booking against what your doctor wrote.
Reading an NS1 result
NS1 is a protein released by the dengue virus. A positive result during the first week means a current or very recent dengue infection.
A negative NS1 is less certain. It does not exclude dengue, which is why doctors pair it with IgM and keep watching your symptoms even after a negative report.
The report should also name the method, usually a rapid card test or an ELISA run in the laboratory. Keep the report so your doctor can see which one was used.
IgM and IgG antibodies
IgM is the antibody the body makes first. A single positive IgM suggests a recent infection, and CDC calls this a presumptive result because IgM can also react to related viruses such as Zika.
IgG can remain in the blood after a past infection. On its own, a positive IgG cannot show whether the dengue is current or from an earlier year, so it is not used by itself to diagnose a new infection.
Tell your doctor if you have had dengue before. WHO notes that a second infection carries a greater risk of severe dengue.
Why the CBC is repeated
The CBC (complete blood count) is not a dengue test in itself. It counts white cells and platelets and measures haematocrit, the share of your blood made up of red cells.
In dengue, white cells and platelets often drop, so doctors follow these numbers over several days. A rising haematocrit can mean fluid is leaking out of the blood vessels, a complication that tends to show up around the time the fever settles.
Keep each report and bring the whole set to every visit, in date order. Repeating the test at the same lab makes the results easier to compare.
Test names and prices
Lab menus usually list "Dengue NS1 Antigen" and "Dengue IgG/IgM" separately, alongside dengue packages that add a CBC. Check what a package contains before you pay for it.
Prices vary between labs, and sometimes between branches of the same lab. Call the branch you plan to visit, ask for the current price of the exact tests on your slip and find out when the report will be ready.
Looking after yourself at home
There is no antiviral medicine for dengue. At home, rest and drink plenty of fluids. Paracetamol helps with fever and pain; take the dose on the pack or the one your doctor gives you.
Do not take ibuprofen or aspirin. WHO advises against these painkillers in dengue because they raise the risk of bleeding.
Dengue mosquitoes bite in the daytime. To protect the rest of the household, cover arms and legs and use repellent. Once a week, empty, scrub and cover anything that holds water: buckets, air cooler tanks, plant pots and old tyres on the roof.
Warning signs: go to hospital
The dangerous phase of dengue often begins after the fever has gone, when it can look as if the illness is over.
Go to a hospital emergency department straight away for severe stomach pain, vomiting that will not stop, fast breathing, bleeding from the gums or nose, or blood in vomit or stool. Restlessness, extreme thirst, pale and cold skin, tiredness and weakness are warning signs as well.
