Molecular methods
Nucleic acid amplification tests (NAAT) can detect dengue virus infections in the first seven days. Reverse transcription-polymerase chain reaction (RT-PCR) can detect dengue virus with a sensitivity of 80–90% and a specificity of 95%. CDC developed the test as a real-time RT-PCR (rRT-PCR) assay that detects serotypes 1–4. A negative NAAT does not rule out dengue infection. Patients should then be tested for the presence of IgM antibodies to determine recent exposure.
Serology
IgM antibody testing can identify most dengue infections after day 3 of illness. These tests are performed on samples with negative NS1 ELISA and PCR results. IgM will be detectable in 50% of cases by three to five days after the onset of symptoms, 80% after day five, and 99% by day ten. The recommended serological test is an IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA). Limitations include that a positive IgM may have cross-reactivity with antibodies to West Nile virus, Yellow Fever virus, Japanese encephalitis virus, and St. Louis encephalitis. Positive patient serum can be confirmed by the Plaque Reduction Neutralization Test (PRNT) for antibodies.
IgG is detectable by ELISA at the end of week one until several months or years later. A titer of 1:1,280 is considered highly suspect by the World Health Organization (WHO). Acute specimens drawn during the first seven days and a convalescent specimen on day ten or later are required to demonstrate a four-fold rise in titer for a definitive diagnosis by serology.
Dengue tests for nonstructural 1 (NS1) glycoprotein antigen and antibody tests have shown cross-reactivity with other flaviviruses.
To diagnose acute dengue, orders should include NS1 ELISA and IgM testing or NAAT and IgM testing.
