The rK39 strip test is non-predictor of clinical status for kala-azar

Abstract

Background: The rK39 strip test is reported to be simple, sensitive, specific, non-invasive and economical test. Since this method is supposed to be patient friendly, it may easily be accepted for sero-epidemiological surveys. An attempt was made to evaluate the role of rK39 strip test in pre and post treatment phases of Kala azar, as a diagnostic and prognostic marker, in addition to other laboratory investigations, in order to evaluate its role in sero-epidemiological surveys. Findings: A total of 210 cases were selected for the study. One hundred clinically and parasitologically confirmed cases were corroborated with other hematological profiles. The formol-gel test was included along with well matched control group comprising of normal endemic controls (50), non-endemic normals (20) and other febrile cases (40). All groups were tested by rK39 strip test. Fifty Kala azar cases were followed up after completion of successful treatment. They were subjected to rK39 strip test after 0, 90 and 180 days of completion of successful treatment. The rK39 showed sensitivity, specificity, PPV, NPV, and diagnostic accuracy of 98% (95% CI 91.7-100), 100%, 100%, 90% (95% CI 66-100) and 98% (95% CI 92.6-100) respectively. All the 50 cured followed up cases showed positive result by rK39 strip test even after 180 days of completion of successful treatment. Conclusion: The test seems an ideal qualitative test for the diagnosis of kala-azar. But for sero-epidemiological studies the test may be used with other parameters. Alternatively a quantitative ELISA using rK39 antigen may be used.