CLINICAL UTILITY OF THE POLYMERASE CHAIN-REACTION IN THE DIAGNOSIS OFINFECTIONS DUE TO MYOBACTERIUM TUBERCULOSIS

Objective: To evaluate the clinical utility of the polymerase chain re action (PCR) in the diagnosis of infections due to Mycobacterium tuber culosis Design: Clinical specimens were assayed by PCR for the presenc e of the insertion element IS6110, a DNA sequence unique to the M tube rculosis complex of organisms. The PCR results were then correlated wi th acid-fast bacilli (AFB) smears, cultures, pathology, and clinical h istories. Setting: Bellevue Hospital, a large municipal teaching hospi tal Patients: Inpatients on the Bellevue Chest Service Measurements an d results: Sixty-five patients were evaluated. The PCR for M tuberculo sis was positive in 37 patients and negative in 28. When correlated wi th smears, cultures, pathology, and clinical history, the sensitivity of PCR for a diagnosis of active tuberculosis (TB) was 100 percent. Ho wever, the specificity for a diagnosis of active TB was only 70 percen t, as the PCR assay was positive in a number of patients with only pri or, treated TB, or asymptomatic tuberculous infection. For a diagnosis of any TB infection (active, treated, or asymptomatic), sensitivity o f PCR was 87.5 percent and specificity was 90 percent. Conclusions: Th e PCR assay for TB is extremely sensitive, but it lacks specificity fo r a diagnosis of active TB. Its role in clinical practice will likely be limited to well-defined situations, such as HIV positive patients w ith intrathoracic adenopathy, and it may be most useful in excluding a ctive TB from consideration in selected patients. Given the cost of th e assay and the labor intensity it requires, it should not be part of the routine initial evaluation of patients with suspected pulmonary TB .