Multi‐centre evaluation of repeatability and reproducibility of the direct agglutination test for visceral leishmaniasis

Abstract

Summaryobjective To evaluate the repeatability and reproducibility of the serological direct agglutination test (DAT) for visceral leishmaniasis (VL) with aqueous antigen in a multi-centre study in VL-endemic areas in Sudan, Kenya and Nepal.methods Repeatability within each centre and reproducibility between the centres' results and an external reference laboratory (Belgium) was assessed on 1596 triplicate plain blood samples collected on filter paper.results High kappa values (range 0.86-0.97) indicated excellent DAT repeatability within the centres. The means of the titre differences between the reference laboratory and the centres in Sudan, Kenya and Nepal (2.3, 2.4 and 1.1, respectively, all significantly different from 0) showed weak reproducibility across centres. 95% of the titre differences between the reference laboratory and the respective centres were accounted for by large intervals: 0.6-9 fold titre variation for Sudan, 0.7-8 fold for Kenya and 0.26-4 fold for Nepal.conclusion High repeatability of DAT confirms its potential, but reproducibility problems remain an obstacle to its routine use in the field. Reproducibility was hindered by alteration of the antigen through temperature and shaking, especially in Kenya and Sudan, and by nonstandardization of the test reading. DAT handling procedures and antigen quality must be carefully standardized and monitored when introducing this test into routine practice. keywords reproducibility, direct agglutination test, visceral leishmaniasis, diagnosis, repeatability, agreement

Operational validation of the direct agglutination test for diagnosis of visceral leishmaniasis.

“…Last but not least, the reliability of the DAT in terms of reproducibility still needs to be formally evaluated. 35 …”

Diagnosis of leishmaniasis

“…Moreover, in settings where parasitological confirmation is not feasible, the freeze-dried DAT together with classical clinical features of VL can be used for diagnosis at a cut-off for positive DAT, which is 1:12,800 as in endemic areas. The DAT is simpler than many other tests but presents severe problems in terms of reproducibility of results, which depends on antigen elaboration [77]. A new antigen elaboration method, the EasyDAT described in 2003, shows the same sensitivity, specificity, and durability as the traditional DAT antigen method but offers the additional advantages of cost reduction and standardization [78].…”

Leishmaniose visceral no Brasil: quadro atual, desafios e perspectivas

“…Na última década, o DAT tem mostrado em vários estudos sensibilidade de 91 a 100% e especificidade de 72 a 100%. A técnica combina altos níveis de validade intrínseca e facilidade de execução, embora apresente problemas na padronização e controle de qualidade do antígeno e não tenha valor no prognóstico da doença 19 . Uma variação da DAT, o FAST (Fast Agglutination Screening Test), vem sendo testada para aplicabilidade em situações epidêmicas e para inquéritos populacionais 20 .…”