Diagnosis of visceral leishmaniasis in Bihar India

Comparison of the rK39 rapid diagnostic test on whole blood versus serum

Citation: Matlashewski G, Das VNR, Pandey K, Singh D, Das S, et al. (2013) Diagnosis of Visceral Leishmaniasis in Bihar India: Comparison of the rK39 Rapid Diagnostic Test on Whole Blood Versus Serum. PLoS Negl Trop Dis 7(5): e2233. doi:10.1371/journal.pntd.0002233
Published: May 23, 2013

AbstractLeishmania_donovani
Background: Antibody-detecting rapid diagnostic tests (RDTs) against rK39 are available to aid in the diagnosis of visceral leishmaniasis (VL). Although these rK39 RDTs have been developed, validated and approved for use with serum, they are universally performed using whole blood. It was therefore necessary to determine whether this RDT is as sensitive on whole blood as on serum.
Method and Principal Findings: In this study we compared the rK39 RDT on serum and blood samples from 624 individuals with symptoms of VL attending the outpatient clinic at the Rajendra Memorial Research Institute of Medical Sciences, Patna, India. A total of 251 cases (40%) were both serum and blood-positive and 26 cases (4%) were identified as blood-negative and serum-positive. These 26 individuals in general had low titer antibodies against rK39 as determined by ELISA and follow-up on most of these individuals revealed none had persistent VL symptoms. The Cohen kappa index comparing blood and serum was 0.88 indicating excellent concordance.
Conclusion: Although the concordance was excellent, it is possible to miss rK39 positive individuals when using blood and the titer of anti-rK39 antibodies is low. We recommend that when an individual from an endemic area has obvious clinical symptoms of VL and the whole blood rK39 RDT is negative, that the test should be redone 2–3 weeks later if the symptoms persist.

Author Summary
Visceral leishmaniasis (VL), is a neglected tropical disease that is highly endemic in the Indian subcontinent and in East Africa and is the second most fatal parasitic disease after malaria. There currently exists several effective treatments for VL and it is therefore essential that the diagnosis be as accessible, sensitive and specific as possible. The current diagnostic test, known as the rK39 rapid diagnostic test (RDT) involves detection of antibodies against the K39 protein antigen from Leishmania. The rK39 RDT was developed for use with serum from potentially infected individuals. However, the test is routinely performed with blood at the community level in the endemic countries because there are no facilities to extract serum from blood. We therefore undertook the present study to compare the sensitivity of the rK39 RDT on serum versus blood from the same potentially infected population from a highly endemic region in Bihar India. Our results show that the concordance between serum and blood was excellent. It was however possible to miss some rK39 positive individuals when using blood. We recommend that when an individual from an endemic area has obvious clinical symptoms of VL and the blood rK39 RDT is negative, that the test should be redone 2–3 weeks later if the symptoms persist.
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