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

Abstract

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/mm 3 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.

Precision Medicine in Control of Visceral Leishmaniasis Caused by L. donovani

“…The rK39 rapid diagnostic tests (RDT) is the only RDT that has been successfully developed in VL; it was found 90% sensitive and 100% specific in India, during a time of high prevalence of VL, and the test is used in the KAEP in the ISC ( Kumar et al., 2001 ). However, false positive results may occur in malaria, tuberculosis, liver cirrhosis and chronic myeloid leukaemia ( Topno et al., 2020 ). In a Cochrane review, the rK39 immunochromatographic test (RDT) showed overall sensitivity in the ISC was 91.9% (95% CI 84.8-96.5) vs 85.3% (95% CI 90.0-99.5%) in East Africa.…”

Demographic characteristics and prevalence of asymptomatic Leishmania donovani infection in migrant workers working in an endemic area in Northwest Ethiopia

“…As expected, a small number of FC and RC tested positive by rK39 RDT. We can not exclude that some of these positive tests might be false positive ( 63 ). No seroconversion of those who tested negative at T1 was observed at T2.…”

Spurious laboratory results associated with immunoglobulin M gammopathy in a dog with multiple myeloma

“…Along with spurious chemistry results, false‐positive serological results occur in humans secondary to paraproteinemia, both because of hematological malignancies (such as multiple myeloma) and secondary to benign age‐related increases in immunoglobulin levels. This includes false‐positive Galactomann antigen tests for aspergillosis, 8,28,29 false‐positive serological tests for syphillis, 5,29,30 and false‐positive rK39 rapid diagnostic tests for leishmaniasis 6 . There are also false‐positive results for a wide range of infectious agents (viral, bacterial, and protozoal) in human patients receiving immunoglobulin therapy IV 31‐35 .…”

“…This includes false-positive Galactomann antigen tests for aspergillosis, 8,28,29 falsepositive serological tests for syphillis, 5,29,30 and false-positive rK39 rapid diagnostic tests for leishmaniasis. 6 There are also false-positive results…”

“…marrow plasmacytosis, and evidence of subsequent organ or tissue impairment (end-organ damage, including bone lesions). 3 Circulating paraproteins in human patients cause spurious laboratory results, 4 including false-positive serological tests, [5][6][7][8] pseudohypoglycemia, [9][10][11] pseudohypophosphatemia, 12 pseudohyperphosphatemia, 13,14 pseudohypercalcemia, 15 falselyelevated C-reactive protein, 16 and altered bilirubin assays. 17 Only sporadic case reports exist in the veterinary literature about the effects of paraprotein interference on laboratory tests, 18,19 and there are no reports documenting false-positive serological tests in the face of paraproteinemia.…”