Utility of PCR in diagnosing pulmonary tuberculosis

Abstract

At present, the rapid diagnosis of pulmonary tuberculosis rests with microscopy. However, this technique is insensitive and many cases of pulmonary tuberculosis cannot be initially confirmed. Nucleic acid amplification techniques are extremely sensitive, but when they are applied to tuberculosis diagnosis, they have given variable results. Investigators at six centers in Europe compared a standardized PCR system (Amplicor; Roche) against conventional culture methods. Defined clinical information was collected. Discrepant samples were retested, and inhibition assays and backup amplification with a separate primer pair were performed. Mycobacterium tuberculosis complex organisms were recovered from 654 (9.1%) of 7,194 samples and 293 (7.8%) of 3,738 patients. Four hundred fifty-two of the M. tuberculosis isolates from 204 patients were smear positive and culture positive. Among the culture-positive specimens, PCR had a sensitivity of 91.4% for smear-positive specimens and 60.9% for smear-negative specimens, with a specificity of 96.1%. Analysis of 254 PCR-positive, culture-negative specimens with discrepant results revealed that 130 were from patients with recently diagnosed tuberculosis and 94 represented a presumed laboratory error. Similar analysis of 118 PCR-negative, culture-positive specimens demonstrated that 27 discrepancies were due to presumed uneven aliquot distribution and 11 were due to presumed laboratory error; PCR inhibitors were detected in 8 specimens. Amplicor enables laboratories with little previous experience with nucleic acid amplification to perform PCR. Disease in more than 60% of the patients with tuberculosis with smear-negative, culture-positive specimens can be diagnosed at the time of admission, and potentially all patients with smear-positive specimens can immediately be confirmed as being infected with M. tuberculosis, leading to improved clinical management.

Polymerase chain reaction test in induced sputum of patients with pulmonary tuberculosis

“…Another reason for this observation could be that the sensitivity of the culture system used in our institution is lower than PCR, as reported previously. [33][34][35][36] Also, when culture is used as the gold standard test, specimens containing non-cultivable organisms may lead to a positive PCR and be considered as false-positive result. 37,38 To support the hypothesis that PCR is more sensitive than culture, it would be useful to have 2 or more positive PCR results in patients with negative cultures, 36 16 demonstrated that the yield of PCR test increased with the greater number of IS samples that were evaluated.…”

Single-Tube Balanced Heminested PCR for Detecting Mycobacterium tuberculosis in Smear-Negative Samples

“…For smear-negative specimens, most published studies report a sensitivity of around 60% or even less, depending on the number of samples and experiment conditions (3,4,7,9,13,16,18,20,24). This low sensitivity for smear-negative specimens shows that current amplification assays may be unsuitable in replacing cultures for the diagnosis of tuberculosis.…”

“…The latter is the most rapid and economic method for detecting mycobacteria. However, given that half of the new cases of TB are smear negative, many diagnoses can not be confirmed at the time of presentation (3). This leads to delays in initiating appropriate treatment and/or the use of invasive procedures to firmly establish the diagnosis.…”

Confirmation of the presence of Mycobacterium tuberculosis and other mycobacteria in mycobacterial growth indicator tubes (MGIT) by multiplex strand displacement amplification

“…Molecular techniques such as PCR and other nucleic acid amplification techniques (NAAT) are capable of detecting and identifying mycobacteria in a few hours. The sensitivities of these NAAT when applied to direct clinical specimen testing have been found to be higher than that of microscopic examination but somewhat lower than that of conventional culture methodology (3,8,19). The cost-effectiveness of performing NAAT on smearpositive specimens seems justifiable since therapeutic and isolation issues can be resolved in a timely manner.…”