Diagnostic value of a nested polymerase chain reaction assay on peripheralblood mononuclear cells from patients with pulmonary and extra-pulmonary tuberculosis

SETTING: Saint Louis Hospital, Paris, France. OBJECTIVE: To determine the clinical relevance of detection of Mycobacteriu m tuberculosis DNA by nested polymerase chain reaction (PCR) in peripheral blood mononuclear cells (PBMCs) in the rapid diagnosis of tuberculosis. DESIGN: Single-centre prospective case study of 90 hospitalised patients an d 50 healthy subjects or blood donors from 1 January to 30 June 1998. RESULTS: Twenty-three patients were diagnosed with tuberculosis (26.7%); 20 tuberculosis patients were culture-positive, with seven smear-positive for acid-fast bacilli. Sensitivity of smear, culture and nested PCR was 30.4 ( 7/23), 87 (20/23) and 30.4% (7/23), respectively. The specificity of smear and culture was 100%, and the specificity of the nested PCR was 96% in the healthy subjects. However, the specificity decreased to 83.6% in the hospit alised patients, with 11 nested PCR-positive patients without a diagnosis o f tuberculosis. The sensitivity of the nested PCR was low in pulmonary tube rculosis (22.2%), but increased in pulmonary/extra-pulmonary tuberculosis ( 50%), extra-pulmonary tuberculosis (33%), and disseminated tuberculosis (33 %). CONCLUSION: The use of a nested PCR assay on PBMC may pose problems for the rapid diagnosis of tuberculosis with regard to low sensitivity and specifi city. However, further studies are needed to confirm this technique as an a lternative test for the diagnosis of paucibacillary forms of tuberculosis.