Title: Comparison of an rK39 dipstick rapid test with direct agglutination test and splenic aspiration for the diagnosis of kala‐azar in Sudan
Abstract: Summary We compared an rK39 dipstick rapid test (Amrad ICT, Australia) with a direct agglutination test (DAT) and splenic aspirate for the diagnosis of kala‐azar in 77 patients. The study was carried out under field conditions in an endemic area of north‐east Sudan. The sensitivity of the rK39 test compared with splenic aspiration was 92% (46/50), the specificity 59% (16/27), and the positive predictive value 81% (46/57). Compared with the diagnostic protocol used by Médecins sans Frontières, the sensitivity of the rK39 test was 93% (50/54), the specificity 70% (16/23), and the positive predictive value 88% (50/57). Compared with splenic aspirates, the sensitivity of a DAT with a titre ≥1:400 was 100% (50/50), but its specificity only 55% (15/27) and the positive predictive value was 80% (50/62). Using a DAT titre ≥1:6400, the sensitivity was 84% (42/50), the specificity 85% (23/27) and the positive predictive value 91% (42/46). All four patients with DAT titre ≥1:6400 but negative splenic aspirate were also rK39 positive; we consider these are probably ‘true’ cases of kala‐azar, i.e. false negative aspirates, rather than false DAT and rK39 seropositives. There were no false negative DATs (DAT titre ≤1:400 and aspirate positive), but there were four false negative rK39 tests (rK39 negative and aspirate positive). The rK39 dipstick is a good screening test for kala‐azar; but further development is required before it can replace the DAT as a diagnostic test in endemic areas of the Sudan.