From the Guidelines
The NS1 rapid test is recommended for diagnosing dengue fever during the early acute phase of infection, specifically within the first 5-7 days after symptom onset. This timing is crucial because the NS1 antigen appears in the bloodstream very early in the infection, often before antibodies develop 1. The test is particularly valuable when patients present with fever, headache, muscle/joint pain, and rash but before serological markers become detectable. NS1 testing offers several advantages: it provides quick results (usually within 15-30 minutes), requires minimal laboratory infrastructure, and can detect infection regardless of serotype. The biological basis for its effectiveness is that the NS1 protein is actively secreted by dengue virus-infected cells during viral replication, making it an excellent marker of active infection. However, clinicians should be aware that NS1 sensitivity decreases after the first week of illness, at which point antibody-based tests (IgM/IgG) become more appropriate for diagnosis. For optimal diagnostic accuracy, NS1 testing may be combined with antibody testing in cases where the duration of symptoms is uncertain.
Some key points to consider when using the NS1 rapid test include:
- The test should be performed on serum, with optimal transport conditions being clot or SST at room temperature, and a transport time of less than 2 hours 1.
- The test is not recommended for use beyond 7 days after illness onset, as sensitivity decreases significantly after this period 1.
- In areas where both dengue and Zika viruses are endemic, consideration should be given to testing for both viruses, as the clinical presentation can be similar 1.
- The use of rapid diagnostic tests, including the NS1 antigen test, can optimize management by reducing unnecessary testing and prescription of unnecessary medications 1.
Overall, the NS1 rapid test is a valuable tool for diagnosing dengue fever, particularly in the early stages of infection, and can be used in conjunction with other diagnostic tests to provide optimal patient care.
From the Research
NS1 Rapid Test for Diagnosing Dengue Fever
The NS1 rapid test is recommended for diagnosing dengue fever in the following situations:
- Early diagnosis of dengue infection, as it can detect the NS1 antigen in the acute phase of the disease 2, 3, 4, 5
- In endemic regions where access to sophisticated diagnostic equipment and trained personnel may be limited 4
- As a screening test to complement current antibody tests used in peripheral laboratories 3
- For detecting NS1 antigen and IgM and IgG anti-antibodies against dengue virus, with good sensitivity and specificity 4
Key Considerations
- The sensitivity of the NS1 rapid test varies, with reported values ranging from 61.6% to 86.0% 2, 4, 5
- The test is highly specific, with reported values of 100% and greater than 87.0% 2, 4, 5
- The test is more sensitive for primary dengue infection than for secondary infection 2
- NS1 positivity is associated with underlying viraemia, with NS1-positive samples having significantly higher viraemia than NS1-negative samples 2
Clinical Applications
- The NS1 rapid test can be used to diagnose dengue fever in patients presenting with symptoms such as fever, headache, and joint pain 3, 6
- The test can be used to detect dengue virus infection in the early stages of the disease, allowing for timely treatment and management 5
- However, the test should not be used as a sole predictor of severe dengue infection, and clinical warning signs should be used to determine the need for hospital admission 6