Abstract
BackgroundRapid immunochromatographic tests (ICT) for dengue non-structural protein 1 (NS1) have shown good performance for diagnosing acute-phase dengue in serum in laboratory settings, but rarely have been assessed in whole blood and at point of care (POC). This study compare the accuracy and inter- and intra-observer reliability of the NS1 Bioeasy™ ICT in whole blood at POC versus serum in the laboratory, during a DENV-1 epidemic.MethodsCross-sectional study involving 144 adults spontaneously demanding care in an emergency department within 4 days of onset of acute febrile illness. Accuracy of NS1 Bioeasy™ ICT was compared in whole blood and serum, both at 15 and 30 min, blinded to the reference RT-PCR or NS1 ELISA. Non-dengue patients were also tested for Zika virus with RT-PCR. Reliability of whole blood and serum readings by the same or different observers was measured by simple kappa (95% CI).ResultsAt 15 min, sensitivity (Sn) of NS1 Bioeasy™ ICT in whole blood/POC was 76.7% (95% CI: 68.0–84.1) and specificity (Sp) was 87.0% (95% CI: 66.4–97.2). Sn in serum/laboratory was 82% (95% CI: 74.1–88.6) and Sp 100% (95% CI: 85.8–100). Positive likelihood ratio was 5.9 (95% CI: 2.0–17.0) for whole blood/POC and 19.8 (95% CI: 2.9–135.1) for serum/laboratory. Reliability of matched readings of whole blood/POC and serum/laboratory by the same observer (k = 0.83, 95% CI: 0.74–0.93) or different observers (k = 0.81, 95% CI: 0.72–0.92) was almost perfect, with higher discordant levels in the absence of dengue. Results did not differ statistically at 5%.ConclusionsNS1 Bioeasy™ ICT in DENV-1 epidemics is a potentially confirmatory test. Invalid results at 15 min should be reread at 30 min. To optimize impact of implementing ICT in the management of false-negatives it should be incorporated into an algorithm according to setting and available specimen.Trial registrationUTN U1111-1145-9451.
Highlights
Rapid immunochromatographic tests (ICT) for dengue non-structural protein 1 (NS1) have shown good performance for diagnosing acute-phase dengue in serum in laboratory settings, but rarely have been assessed in whole blood and at point of care (POC)
The current study aimed to compare the accuracy and reliability of NS1 BioeasyTM ICT in whole blood at POC and in serum in the laboratory in adults during a Dengue virus (DENV)-1 epidemic in Rio de Janeiro State, Brazil. This was a prospective diagnostic cross-sectional study that evaluated accuracy of the NS1 BioeasyTM rapid immunochromatographic test and inter- and intraobserver reliability in whole blood specimens at point of care (POC) and serum specimens in the laboratory
Four samples that were negative for dengue by Reverse Transcription Polymerase Chain Reaction (RT-PCR) and NS1 Enzyme-linked immunosorbent assay (ELISA)
Summary
Rapid immunochromatographic tests (ICT) for dengue non-structural protein 1 (NS1) have shown good performance for diagnosing acute-phase dengue in serum in laboratory settings, but rarely have been assessed in whole blood and at point of care (POC). Clinical suspicion of dengue is based on the signs and symptoms described in the World Health Organization (WHO) guidelines, i.e., nausea/vomiting, rash, aches and pains, leucopenia, any warning sign (abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy/restlessness, liver enlargement, and hemoconcentration concurrent with rapid decrease in platelet count). This criterion shows low specificity due to the absence of confirmatory laboratory tests [4]. The World Health Organization (WHO) recommends that ideal laboratory diagnostic tests should be affordable, sensitive, specific, user-friendly, robust, rapid (can be stored at room temperature and interpreted within 30 min), equipment-free, and deliverable to those who need them (ASSURED) [6]
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