Evaluation of a new serodiagnostic tuberculosis test based on immunoglobulin A detection against Kp-90 antigen

We evaluated a new serological test for tuberculosis (TB) diagnosis, an enzyme-linked immunosorbent assay which detects the presence of immunoglobulin A (IgA) antibodies in human serum, the Kreatech TB IgA EIA test. The study was performed using 166 serum samples collected in the city of Barcelona, Spain. Fifty-six serum samples were from TB patients and 111 from controls, 40 of which were non-TB pneumonia patients. The test sensitivity was 70.58% in the adult group with pulmonary TB and 50% in the group with extra-pulmonary TB. These sensitivities were similar to those previously reported by others. However, we found that the test had a low specificity of only 68.68%, while specificities of 90% and 95% have been reported. This discrepancy may be attributable to differences in the respective study populations. In our control group we included 40 non-TB pneumonia patients (36% of the entire control group), in whom test specificity dropped to 47.22%. In those studies in which specificities of 90% and above were achieved, very few serum samples from non-TB pneumonia patients were tested (6-12% of the entire control group).