Anti-Kp 90 IgA antibodies in the diagnosis of active tuberculosis

Background: Accurate diagnosis of active tuberculosis (TB) has been difficult historically, yet a great demand persists for a rapid and reliable diagnostic method. Detection of Mycobacterium tuberculosis anti-Kp 90 IgA antibodies is one of the more novel techniques. Study objectives: To evaluate the diagnostic value of a recently developed enzyme-linked immunosorbent assay (ELISA) test, which detects IgA antibodies against M tuberculosis Kp 90 antigen, and to compare the results with conventional diagnosis and the polymerase chain reaction (PCR) method. Participants: Serum, ethylenediaminetetraacetic acid (EDTA)-blood, and body fluid samples were obtained from 51 patients with active TB and 71 control subjects. The clinical diagnosis of TB was supported by a positive culture (n = 6), detection of acid-fast bacilli on smear (n = 35), or both (n = 10). Measurements and results: IgA antibodies were detected in sera and/or body fluid samples from 82% of patients with TB and 10% of controls. M tuberculosis DNA was detected in body fluid sample of 96% and blood sample of 49% of patients with TB by PCR. None of the blood and 5.6% of the body fluid specimens from controls were PCR-positive. Conclusions: Anti-Kp 90 IgA antibodies were detected using ELISA in 78% of serum and 69% of body fluids from patients with TB, therefore, this test is promising for the diagnosis of active TB and appears to be more reliable, particularly for body fluid samples.