VHOSPITAL.CLINIC · Diagnostic Test
The rK39 rapid diagnostic test delivers a result in 10 minutes from a finger-prick blood sample and is the WHO-endorsed point-of-care test for visceral leishmaniasis — achieving >97% sensitivity in South Asia.
The rK39 antigen (a 39-amino acid repeat of a kinesin-related protein from L. chagasi) is highly immunogenic in visceral leishmaniasis. The lateral flow strip test detects anti-rK39 IgG antibodies — absent in healthy individuals and those with cutaneous leishmaniasis.
A finger-prick blood sample (10–15 μL) is applied to the test cassette with buffer. A visible line at the test position within 10 minutes indicates positive. The control line must always appear for a valid result. No laboratory equipment needed — suitable for field use.
Positive: anti-rK39 antibodies detected — consistent with active or recent visceral leishmaniasis (clinical correlation required). Negative: VL unlikely, but consider serology (ELISA) if clinical suspicion is high. The rK39 RDT has lower sensitivity in East Africa (75–85%) vs South Asia (>97%) — regional performance varies significantly.
Sensitivity: 97–100% in India/Bangladesh; 75–85% in East Africa (Kenya, Ethiopia). Specificity: 95–98% globally. The rK39 test remains positive for months after successful treatment — cannot be used to confirm cure. Concurrent HIV infection reduces sensitivity to ~75%.
L. donovani strains causing VL in East Africa differ genetically from those in South Asia, causing different antibody profiles. The rK39 antigen originated from L. chagasi (South American/South Asian clade) and is less immunogenic in East African infection — leading to 75–85% sensitivity in Ethiopia/Sudan vs 97–100% in India.
No. rK39 antibodies persist for 6–24 months after successful treatment. A positive test post-treatment does not indicate treatment failure. Clinical assessment (fever resolution, weight gain, spleen regression) and follow-up CBC are used to assess treatment response.
Rarely. The rK39 antigen is highly specific for visceral infection — patients with cutaneous or mucosal leishmaniasis typically test negative because the antibody response is weaker and different species are involved. A positive rK39 in a patient with skin lesions suggests systemic involvement.
rK39 Rapid Diagnostic Test helps confirm Leishmaniasis, which can cause these symptoms:
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