3.3 Dengue Diagnostic Test

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Detection of Antigen: NS1 antigen (non-structural protein 1):

  • NS1 antigen rapid test- positive within minutes of starting symptoms.
  • The ELISA NS1 antigen will be positive on first day of illness.
  • This test becomes negative from day 4-5 of illness.
  • Commercial kits for the detection of NS1 antigen are now available in ELISA or rapid test format.

Dengue IgM /IgG test (MAC ELISA or Rapid ICT):

  • Anti-dengue IgM specific antibodies can be detected after 5 days of the onset of fever and highest level achieved after 7 days.
  • It can be detected in low level up to 1-3 months after fever.
  • In primary dengue infection- IgM will be more than IgG early period and sed IgG at 9 or 10th day of fever. Level of this IgG may persist at low levels for decades, indicating past dengue infection.
  • In secondary dengue infection- higher elevation of anti-dengue specific IgG antibodies and lower levels of IgM. The higher IgG levels remain for 30–40 days.
  • Rapid ICT test provides result within 15 to 20 minutes.

Nucleic Acid Detection:

  • The reverse transcriptase polymerase chain reaction (RT-PCR)- confirm diagnosis (<5 days of illness).
  • The amplified DEN viral RNAs can be detected either by tradition or real time PCR.
  • This test is expensive and available only in referral centers.

Dengue Virus Isolation:

  • Dengue virus isolation from serum, plasma and leucocytes is the most definitive test for dengue infection, which can be accomplished in majority of cases if the sample is taken in the first few days of illness.
  • Isolation of dengue virus from serum, CSF or autopsy samples.
  • Detection of dengue virus or antigen in tissue, serum or cerebrospinal fluid by immunohistochemistry, immunofluorescence or enzyme-linked immuno-sorbent assay.
  • Detection of dengue virus genomic sequences by reverse transcriptionpolymerase chain reaction.

Tests for objective evidence of dengue infection are not helpful for guiding the management. NS1 (nonstructural protein) rapid antigen is an excellent test for confirmation of dengue syndrome.

Table 3 - Time & Frequency of Investigation

Available Dengue Diagnostic Tests at Different Level of Health Care Centers:

Primary Health care: For diagnosis and surveillance purpose, at primary-health care level, rapid tests for Dengue specific IgM/ IgG and dengue NS1 antigen should be used.

Secondary Health care: At district health centers, both ELISA and rapid tests for detection of antigen and antibody can be performed.

Tertiary health care: All diagnostic methods should be available at refer centers, including virus isolation, nucleic acid detection and all serological technique.

Table 4 - Dengue Diagnostic Service Delivery Level

ELISA = enzyme-linked immunosorbent assay; IgG= immunoglobulin G; IgM =immunoglobulin M; IHA = indirect haemagglutination; NS1 Ag = non-structural protein 1

Table 5 - Confirmed and probable dengue diagnosis, interpretation of results and sample characteristics