The DUAL IT L/M rK39 antigen-based dipstick from DiaMed AG, Switzerland, was found to be highly sensitive (97%) and specific (97%) for the diagnosis of VL in northeastern Uganda. The Kalazar Detect dipstick was also highly specific (99%) but substantially less sensitive (82%). The FGT was less sensitive (66%) and specific (90%) than the rK39 dipsticks.
Our study is the first to evaluate the performance of these tests in Uganda and is one of the few diagnostic accuracy studies in VL using a prospective design in a clinical setting (23
). The reference standard we used was a composite one: case ascertainment was based either on direct examination of Giemsa-stained splenic aspirates smears (close to 100% sensitivity and specificity) or on a combination of serology with observation of response to treatment. The diagnostic accuracy of DAT is known to be excellent and, since the therapeutic spectrum of antimonials is so narrow, a good response to it can safely be regarded as evidence of visceral leishmaniasis (25
). All DAT results and spleen aspirates were reviewed in reference laboratories, and patients with discordant results were excluded from analysis. Therefore, we can safely claim that little or no misclassification occurred in the present study with regard to disease status.
The DiaMed-IT LEISH, the equivalent of the DUAL IT L/M but without the malaria diagnostic component, has been previously evaluated in India and Sudan. In India, the sensitivity of the DiaMed-IT LEISH was 99% and its overall specificity was 94% when tested on blood from patients with VL, patients with other diseases, and controls from areas of high and low endemicity (20
). In Sudan, the DiaMed-IT LEISH was found to be 81% sensitive and 97% specific in a group of 341 clinical suspect individuals (16
). Low sensitivity of rK39 antigen-based dipsticks was already reported in another study from Sudan, and the authors of that study suggested that Sudanese VL patients develop lower titers of antibodies against the K39 antigen (27
). Other researchers suggest that the format of the immunochromatographic assay might be the cause (16
). Therefore, we believe that the results of diagnostic accuracy studies for VL should only be extrapolated with caution between different epidemiological and ecological regions.
The Kalazar Detect dipstick from Inbios International, Inc., Seattle, Wash., has been previously evaluated (sometimes under another trade name) in the Indian subcontinent and Latin America, with reported sensitivities and specificities of 87 to 100% and 71 to 100%, respectively (5
). The present study is the first published evaluation of the validity of the Kalazar Detect among African patients clinically suspect of VL. We found a disappointingly low sensitivity (81%) but an excellent specificity (99%). An ongoing multicenter diagnostic study conducted by the World Health Organization in several East African countries will add data on the validity of the Kalazar Detect. According to the manufacturer, a more sensitive generation of the Kalazar Detect dipstick is under development.
The poor sensitivity of the FGT confirmed the findings of previous studies (5
). The specificity of the FGT was good (90%) but lower than recently described in Nepal (5
), most likely because hyper-reactive malarial syndrome, a classical cause of polyclonal hypergammaglobulinemia, was a frequent diagnosis (61%) in our non-VL patients. We considered the diagnostic performance of the FGT in this setting insufficient to recommend its use. Eleven percent of persons with a positive FGT would be wrongly started on antileishmanial therapy, an unacceptable proportion considering the heavy burden on the patient of 1 month of parenteral therapy and the relative toxicity and high cost of branded antimonials (Pentostam), the current first-line treatment in use in Uganda. Also, 34% of true kala-azar patients would be missed by the FGT, an unacceptably high proportion.
Practical issues in the utilization of the two rK39 dipsticks also need to be considered. A major advantage of the DUAL IT L/M is that it can be performed with blood obtained by fingerprick. Moreover, all test components are included in individual packages. In contrast, the Kalazar Detect is performed with serum, requiring sampling of venous blood and extra materials such as a micropipette and test tubes. Another advantage of the DUAL IT L/M is that the test result remains stable and can be read up to several months later. This allows for external quality control when the test is performed at peripheral health units by workers with limited training. According to the manufacturers, the cost per unit of the Kalazar Detect and the DUAL IT L/M dipsticks for developing countries is $1.00 and $1.30 (U.S. dollars), respectively. This represents a very small fraction of the total expenses needed to manage patients with VL since the cost of test and treatment strategies depends mainly on the cost of hospitalization and treatment (4
). The relatively high packaging volume of the DUAL IT L/M can indirectly increase transport cost if high numbers of dipsticks are needed.
We found no added value of the malaria antigen (pLDH) detection line present on the DUAL IT L/M in our population of VL suspect patients. Only few non-VL patients were diagnosed with smear-proven malaria (8.4%), and the sensitivity of the DiaMed DUAL IT L/M among these patients was only 57%. This poor sensitivity was most likely due to the high proportion (43%) of patients with low parasitemia (<200 parasites/mm3
). A low sensitivity of the Optimal test (DiaMed AG, Switzerland), using the same technology, has been previously reported in malaria patients with low parasitemia (15
). It must be emphasized that malaria has a clear seasonal pattern in the study area and that our study took place during a low-transmission season. The prevalence of smear-proven malaria and the intensity of parasitemia is likely to be higher during the high-transmission rainy season, thus influencing the performance of the malaria component of the DUAL IT L/M.
In summary, the DUAL IT L/M was found to be a highly accurate and practical diagnostic test for VL in Uganda. The malaria diagnostic component was not found to be useful. Therefore, we introduced the DiaMed IT LEISH as a first-line test for patients presenting with clinical suspicion of VL at AH in the first trimester 2005. If an ongoing 3- to 6-month post-study validation phase confirms the findings of the present study, the dipstick will replace the DAT for the diagnosis of VL in this setting in Uganda. Because of the long persistence of antibodies against rK39 antigen in the serum after treatment (27
), spleen puncture will remain necessary to confirm the diagnosis of relapse in patients with a previous history of VL and a positive dipstick. The introduction of the dipstick in more peripheral health centers, leading to an earlier diagnosis and perhaps a better treatment outcome, should then be implemented. The major remaining challenge is for the Ugandan Ministry of Health to create and ensure a sustainable supply of this diagnostic tool to AH.