Detection of Mycobacterium tuberculosis in serum samples using the polymerase chain reaction

Conventional methods for the diagnosis of Mycobacterium tuberculosis infections have serious limitations. To determine whether amplification of M. tuberculosis DNA in serum by the polymerase chain reaction (PCR) might be a useful additional diagnostic tool, we tested 329 clinical specimens using primers specific for the IS6110 insertion sequence of the M. tuberculosis complex. The samples consisted of 30 serum samples from healthy controls, 114 serum samples from patients with diagnoses other than tuberculosis (including immunosuppressive disorders), 59 samples from patients with a clinical picture suggestive of tuberculosis, and 78 serum samples from patients with proven M. tuberculosis infection. Both serum, and representative samples from anatomical regions suspected of being infected, were collected from a further 48 patients for comparison with serum PCR. Serum PCR identified 72/78 (92%; 95% confidence interval CI: 84%-97%) patients with proven tuberculosis, and 49/59 (83%; 95% CI: 71%-92%) patients with suspected tuberculosis. In the group of patients with other diagnoses, 30/114 (26%; 95% CI: 18%-34%) tested positive, while none of the specimens from the healthy control group were positive (95% CI: 0%-12%). Serum PCR results also compared favourably with other clinical specimens obtained from the same patient. Serum PCR can, therefore, be a useful additional technique for the early diagnosis of M. tuberculosis infection, but it does not necessarily indicate active infection.