POLYMERASE CHAIN-REACTION IN THE DIAGNOSIS OF URINARY-TRACT TUBERCULOSIS

The polymerase chain reaction (PCR) is a technique that can be used to amplify a specific DNA genomic sequence, whereby the presence of an e xtremely small number of bacteria can be detected. The high sensitivit y of PCR is particularly useful in paucibacillary situations such as n on-pulmonary tuberculosis (TB). The aims of the present study were to establish a PCR assay for the rapid detection of Mycobacterium tubercu losis (MTb) in urine, to compare the sensitivity of PCR with routine c ulture technique (Bactec) and to determine the optimal type of urine s pecimen for PCR detection of MTb. In the first phase of the study, a t otal of 92 urine specimens were collected from 83 patients with suspec ted urinary tract TB. Two urine specimens in 2 patients were positive for TB by both PCR and Bactec, while 90 specimens from 81 patients wer e negative by both methods. Inhibition of PCR was present in nine urin e specimens (10%). In the second phase of the study, a further seven p atients were selected for intensive investigation to determine the opt imal urine sampling for PCR detection of MTb. The conclusions of the s tudy are that PCR can provide much faster confirmation of urinary TB ( within 24-48 h) than Bactec urine culture (which may take several week s). About 10% of urine specimens could not be evaluated by PCR due to the presence of inhibitory substances of unknown nature. MTb organisms were found to be excreted intermittently in the urine of infected pat ients, and single specimens were more likely to be false negative than a 24-h sample. The best method appeared to be the concentration of a large volume of urine, for instance 1 l concentrated to 2 ml.