Dengue Diagnostics

Laboratory Tests and Ancillaries

Detection of Antigens  

Developments in ELISA and dot blot assays directed to the envelope/membrane (E/M) antigen and the non-structural protein (NS1) showed that high concentrations of these antigens (immune complexes) could be detected in patients during the early period of the disease and in patients with primary and secondary dengue infections up to 6 days after the start of illness.  

Non-structural protein 1 (NS1) ELISA has been shown to be a useful diagnostic tool in acute dengue infections. It is produced by all flaviviruses and is secreted from mammalian cells. Dengue NS1 antigen has been detected in the serum of dengue virus-infected patients as early as one-day post-symptom onset (PSO) and up to eighteen days post onset (DPO). It may also be useful for differential diagnosis between flaviviruses because of its specificity. NS1 antigen detection kits are commercially available and can be used by laboratories with limited equipment and yield results within a few hours.  

Serology  

The HI test is a simple, sensitive, and reproducible test that requires paired sera, soon following hospital admission (acute) and 10-14 days after discharge (convalescent). A titer of ≥1:1280 in an acute or convalescent phase serum sample is considered presumptive evidence of current dengue. It is negative in an early acute blood specimen and a repeat specimen should be tested before confirming or excluding dengue infection. It is limited by its inability to discriminate between infections by closely related flaviviruses.  

IgM antibody capture-ELISA (MAC-ELISA) is the serological test of choice because the ELISA IgM detected is specific for flavivirus. It is rapid and simple, and it only requires a little sophisticated equipment. A single, properly timed blood sample may be adequate. A high increase in the molar fraction of IgM indicates a primary acute flavivirus infection and a low increase in the molar fraction of IgM indicates a secondary acute flavivirus infection. A high IgM antibody response indicates a recent primary flavivirus infection and a low IgM antibody response indicates a recent secondary flavivirus infection.  

In MAC-ELISA, a positive dengue IgM result indicates acute or recent past infections (up to 90 days). A single positive dengue IgM may not be indicative of present dengue infection. MAC-ELISA may also be used to detect CSF IgM. However, it cannot be used to identify infecting virus serotypes. Positive results do not necessarily denote a current dengue infection. Caution must be exercised when making decisions about patient management.  

IgG ELISA is comparable to the HI test and can be used to differentiate primary and secondary infections.  

The neutralization test (NT) is the most specific and sensitive serologic test for dengue virus. It is not commonly used because it is expensive, requires a long time for performance, and is technically difficult. Serum dilution plaque reduction NT is the most common protocol.  

The complement fixation (CF) test is the least sensitive serological assay. It appears later than IgM or HI antibody and is usually less specific. It has greater specificity for primary infections but is not specific in secondary infections.  

Other Laboratory Tests for Dengue Patients  

CBC may show normal total WBC, but leukopenia may develop throughout the febrile period. The mild increase in hematocrit may be due to dehydration. Platelet counts and factors of the blood clotting mechanism can be normal. Thrombocytopenia may occur.  

Albumin level is usually low. Liver function tests such as ALT and AST levels should be evaluated. Urinalysis may be requested to check for hematuria.  

Other diagnostic tests include virus isolation. There are also molecular techniques including reverse transcriptase-polymerase chain reaction (RT-PCR). Its specificity and sensitivity are better than virus isolation with a faster turnaround time.