What are the primary diagnostic tests for a patient suspected of having dengue (Dengue virus infection)?

Diagnostic Tests for Suspected Dengue

For a patient with suspected dengue infection, the primary diagnostic tests include nucleic acid amplification tests (NAATs), NS1 antigen detection, and serological testing for IgM and IgG antibodies, with the choice of test depending on the timing of symptom onset. 1

Diagnostic Testing Based on Timing of Symptoms

Early Phase (≤7 days after symptom onset)

• Dengue virus NAAT (PCR) - Most sensitive during the first week of illness when viremia is present 1
• NS1 antigen detection - Can be detected as early as day 1 after symptom onset and remains positive during the first week of illness 2
• IgM antibody testing - May begin to appear by day 3-5 of illness 1, 3

Late Phase (>7 days after symptom onset)

• IgM antibody testing - Primary diagnostic method after the first week of illness 1
• IgG antibody testing - Useful for determining primary versus secondary infection 1, 3
• Plaque reduction neutralization tests (PRNTs) - Confirmatory testing to resolve false-positive IgM results or distinguish between dengue and other flavivirus infections 1

Interpretation of Test Results

Positive Diagnostic Results

• Positive dengue virus NAAT indicates acute dengue virus infection 1
• Positive NS1 antigen confirms dengue infection during the acute phase 2
• Positive dengue IgM antibody with negative Zika virus IgM and PRNT ≥10 against dengue virus with negative PRNTs against other flaviviruses indicates recent dengue virus infection 1

Negative Results

• Negative dengue and Zika virus NAATs in specimens collected ≤7 days after symptom onset should be followed by IgM antibody testing 1
• Negative PRNT titers against dengue and Zika virus in serum collected >7 days after illness onset rule out infection with either virus 1

Additional Laboratory Tests for Clinical Management

• Complete blood count - Monitor for thrombocytopenia, which is common in dengue infection 4, 5
• Liver function tests - Assess for hepatic involvement, which correlates with disease severity 5, 6
  • SGOT/SGPT elevations are seen in 74.2% of dengue patients and increase with disease severity 5
• Coagulation profile - PT, aPTT, and TT to assess for coagulopathy 4
• Albumin levels - Hypoalbuminemia is more common in severe dengue (50.8%) 5

Imaging Studies

• Abdominal ultrasonography - To detect plasma leakage manifestations such as:
  • Gallbladder wall thickening 6
  • Ascites - More common in DHF (76.9%) and DSS (72%) 6
  • Pleural effusion - More common in DHF (73.1%) and DSS (68%) 6

Diagnostic Algorithm for Suspected Dengue

1. For patients presenting ≤7 days after symptom onset:

   • Perform dengue virus NAAT and/or NS1 antigen testing 1, 2
   • If negative, perform dengue IgM antibody testing 1

2. For patients presenting >7 days after symptom onset:

   • Perform dengue IgM antibody testing 1
   • If positive, consider confirmatory PRNT if needed to distinguish from other flavivirus infections 1

Common Pitfalls in Dengue Diagnosis

• Cross-reactivity - IgM antibodies may cross-react with other flaviviruses (e.g., Zika, West Nile, yellow fever) 1
• Timing of specimen collection - False negatives can occur if specimens are collected too early or too late relative to symptom onset 2
• Secondary infections - May have atypical serological responses with rapid rise in IgG and diminished IgM response 1, 3
• NS1 antigen false negatives - May occur very early in infection or later in the disease course, especially in secondary infections 2

Application to the Case

For the 9-year-old female patient with 5 days of intermittent fever, the positive IgM on day 4 of illness supports the diagnosis of dengue infection 1. Her clinical presentation with fever, myalgia, headache, abdominal pain, and hypotension is consistent with dengue fever progressing to early signs of shock, requiring close monitoring for plasma leakage and other complications 5, 6.