False Positivity of rK39 Test in Five Chronic Myeloid Leukemia Cases from Bihar, India: A Possible Challenge to Leishmaniasis Diagnosis.

A rapid and noninvasive rK39 rapid diagnostic test (RDT) is the best and most reliable tool for visceral leishmaniasis (VL) screening in the field. However, splenic and bone marrow aspiration remain two gold standard methods for microscopic identification of Leishmania donovani (LD) bodies and confirmatory diagnosis of VL. Five patients with signs and symptoms of fever, loss of appetite, loss of weight, hepatomegaly, and massive splenomegaly were found to be false positive with the rK39 RDT. These patients were suspected to have chronic myeloid leukemia (CML) because their blood pictures showed a total white blood cell count of > 100,000/mm3 and abnormal cells such as stab, segmented promyelocytes, myelocytes, metamyelocytes, and blast cells. Splenic aspirate and bone marrow were negative for Leishmania donovani bodies. The bone marrow showed myeloid series of cells, that is, myelocytes, metamyelocytes, stab and segmented cells, blast cells, and markedly increased myeloid:erythroid ratio. Later, the CML diagnosis was confirmed in all cases by breakpoint cluster region-tyrosine protein kinase (BCR-ABL) gene positive test results. In this study, the rK39 RDT's false positivity was observed in CML cases. It could have important implications for the differential diagnosis of VL with CML. The rK39 positive test result in CML cases was a serendipitous occurrence; this should be validated further to determine the utility of the rK39 test in the differential diagnosis of VL with CML.