Tests
1st tests to order
CBC
Test
Should be ordered initially in all symptomatic patients in resource-poor and resource-rich regions.
Leukopenia and thrombocytopenia typically occur as early as the second day of fever.[1] Leukopenia (with neutropenia) persists throughout the febrile period.
In classical dengue fever, thrombocytopenia is usually mild, although it also may be severe.[1]
Hematocrit may also rise approximately 10% in patients with DF due to dehydration.[1]
A rapid decrease in platelet count and elevated hematocrit is a warning sign that indicates a patient with dengue infection is about to enter the critical phase of infection.[2][15]
Rapidly developing severe thrombocytopenia, decreased total WBC and neutrophils, changing neutrophil-to-lymphocyte ratio, and elevated hematocrit (i.e., 20% increase from baseline is objective evidence of plasma leakage) supports a diagnosis of dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS).[1][2]
Result
leukopenia; thrombocytopenia; elevated hematocrit
liver function tests (LFTs)
Test
Should be ordered initially in all symptomatic patients in resource-poor and resource-rich regions.
Usually elevated, particularly alanine and aspartate aminotransferases.[1]
An aspartate aminotransferase (AST):alanine aminotransferase (ALT) ratio >2 supports a diagnosis of DHF/DSS.[1][2]
Result
elevated
serum albumin level
serology
Test
Generally more readily available in dengue-endemic regions and are the test of choice in these areas, especially when other tests are not available. Whole blood, serum, or plasma specimen can be used.
Serology may be negative in the first 5 days of illness; therefore, IgM enzyme-linked immunosorbent assay (ELISA) and IgG ELISA are the serologic tests of choice after the first 5 days of illness (polymerase chain reaction [PCR] is more sensitive in the first 5 days). The presence of IgG in the first few days of infection strongly suggests a secondary infection.
IgM rapid tests are commercially available and easy to use; however, their accuracy is poor as cross-reaction with other infectious agents and autoimmune disorders can occur.
Hemagglutination-inhibition (HI) test is useful for diagnosing secondary dengue infection (i.e., titer ≥1:1280).
Advantages: inexpensive, easy to perform, more readily available in dengue-endemic areas, can distinguish between primary and secondary infection.[2]
Disadvantages: lower specificity compared to other tests, requires 2 serum samples, delays confirmation of diagnosis.[2]
Confirmatory testing recommendations vary between countries. These recommendations are based on guidance from the World Health Organization. The Centers for Disease Control and Prevention (CDC) recommendations differ.[81] Consult your local guidance for more information.
Result
positive IgM and IgG in a single serum sample (highly suggestive of infection); IgM or IgG seroconversion in paired sera or a fourfold IgG titer increase in paired sera (confirms infection); IgM:IgG ratio <1.2 (suggests secondary infection); negative result does not exclude infection unless paired sera are tested
reverse transcription-polymerase chain reaction (RT-PCR)
Test
Test of choice for viral nucleic acid detection and can be ordered within the first 5 to 7 days of illness. Tissue, whole blood, serum, plasma, or cerebrospinal fluid specimens can be used.[80]
Conventional PCR takes about 5 to 8 hours; newly developed rapid methods can give a result in 2 to 3 hours.
May not be available in dengue-endemic regions.
Advantages: the most sensitive and specific test available, especially in early infection; early diagnosis is possible, which may impact management; can identify serotype.[2]
Disadvantages: expensive; requires laboratory facilities and expertise; cannot differentiate between primary and secondary infection; potential for false-positive result due to contamination.[2]
Confirmatory testing recommendations vary between countries. These recommendations are based on guidance from the World Health Organization. The Centers for Disease Control and Prevention (CDC) recommendations differ.[81] Consult your local guidance for more information.
Result
positive
nonstructural protein 1 (NS1) detection
Test
Detection of the nonstructural protein 1 (NS1) using ELISA or rapid kits is useful in early diagnosis and can be ordered from days 1 to 9 of the illness.[79] A serum specimen should be used.
May not be available in dengue-endemic regions.
Advantages: easy to perform; rapid tests can be used in the field and provide results in a few hours; early diagnosis is possible, which may impact management.[2]
Disadvantages: may be as sensitive as viral nucleic acid detection; however, does not identify serotype.[2]
Confirmatory testing recommendations vary between countries. These recommendations are based on guidance from the World Health Organization. The Centers for Disease Control and Prevention (CDC) recommendations differ.[81] Consult your local guidance for more information.
Result
positive
Tests to consider
coagulation studies
Test
Not required for diagnosis but may play a useful role in the management of infection in patients with hemorrhagic signs.
Prolonged prothrombin time and activated partial thromboplastin time were increased in 16.5% and 42.9% of patients with dengue fever, respectively.[88]
Result
variable
chest x-ray
Test
Only required if DHF/DSS is suspected.
A lateral decubitus chest x-ray of the right-hand side of the chest can be ordered to detect clinically undetectable pleural effusion in the early phase of plasma leakage.
Result
blunting of the costophrenic angles in erect position (severe disease)
abdominal ultrasound
Test
Only required if DHF/DSS is suspected.
May be ordered to detect the presence of ascites or other pathologic changes in abdominal organs, including the liver, gallbladder (i.e., edema may precede plasma leakage), and kidneys.[1][2]
Result
may show ascites, abnormalities of liver/gallbladder (severe disease)
Emerging tests
reverse transcription-insulated isothermal polymerase chain reaction (RT-iiPCR)
Test
A newly developed pan-dengue virus RT-iiPCR in combination with a nucleic acid analyzer, may provide a highly reliable, sensitive, and specific point-of-need diagnostic assay in the future.[83]
Result
positive
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