How Is It Used?
Dengue fever testing is used to determine whether a person with symptoms and recent potential exposure to dengue has been infected. The infection is difficult to diagnose without laboratory tests because symptoms may initially resemble other diseases, such as malaria. Two types of testing are available:
- Antibody tests
These tests are primarily used to help diagnose a current or recent infection. They detect two different classes of antibodies produced by the body in response to a dengue fever infection, IgG and IgM.
Diagnosis may require a combination of these tests because the body’s immune system produces varying levels of antibodies over the course of the illness. IgM antibodies are produced first and tests for these are most effective when performed at least 7-10 days after exposure.
Levels in the blood rise for a few weeks, then gradually decrease. After a few months, IgM antibodies fall below detectable levels. IgG antibodies are produced more slowly in response to an infection. Typically, the level rises with an acute infection, stabilizes, and then persists long-term.
Individuals who have been exposed to the virus prior to the current infection maintain a level of IgG antibodies in the blood that can affect the interpretation of diagnostic results.
- Molecular testing (polymerase chain reaction, PCR)
This type of test detects the genetic material of the dengue virus in blood up to 5 days after symptom onset (fever).
When Is It Ordered?
Testing may be ordered when individuals have signs and symptoms associated with dengue following travel to tropical locations where the virus is present. Some of the main signs and symptoms include:
- Sudden high fever (104°F or 40°C)
- Severe headache or pain behind the eyes
- Joint, muscle and/or bone pain
- Gum and nose bleeds
- Easy bruising
- Low white blood cell count
Testing is usually ordered within one to two weeks of the onset of symptoms to detect an acute infection. If antibody testing is performed, an additional blood sample may be collected after two weeks of symptoms to determine if the antibody level is rising.
What Does The Test Result Mean?
Antibody testing—antibody tests may be reported as positive or negative, or may be reported as an antibody titer with an interpretation of which type(s) of antibody (IgG or IgM) is present.
Positive IgM and IgG tests for dengue antibodies detected in an initial blood sample mean that it is likely that the person became infected with dengue virus within recent weeks. If the IgG is positive but the IgM is low or negative, then it is likely that the person had an infection sometime in the past. If the dengue IgG antibody titer increases four-fold or greater (e.g., titer of 1:4 to a titer of 1:64) between an initial sample and one taken 2 to 4 weeks later, then it is likely that a person has had a recent infection.
Negative tests for IgM and/or IgG antibodies may mean that the individual tested does not have a dengue infection and symptoms are due to another cause, or that the level of antibody may be too low to measure. The person may still have a dengue infection – it may just be that it is too soon after initial exposure to the virus to produce a detectable level of antibody.
The following table summarizes results that may be seen with antibody testing:
|IgM Result||IgG Result||Possible Interpretation|
|Low or negative or not tested||Four-fold increase in samples taken 2-4 weeks apart||Recent infection|
|Low or negative||Positive||Past infection|
|Negative||Negative||Too soon after initial exposure for antibodies to develop or symptoms due to another cause|
Molecular testing—a PCR test that detects the presence of the virus itself is generally considered the most reliable means of diagnosis, but the test is not widely available. A positive result from a PCR is considered conclusive. A negative result on a PCR test may indicate that no infection is present or that the level of virus is too low to detect, as may happen if the test was performed after the 5-day window during which the virus is present in the sample collected for this test. If very recent exposure is suspected, repeating the test at a later time may be warranted.
Is there anything else I should know?
Physical symptoms like rash or aching joints are not a reliable means for diagnosing dengue fever because the symptoms are not likely to appear until after the initial fever has passed.
Antibody tests for dengue fever can be positive if a person is infected with another arbovirus such as West Nile virus. A health practitioner will consider a person’s test results, medical history, and recent travel history in making a diagnosis.
No laboratory test can predict whether or not the infection will progress to the more severe form.