Use of the Bac-T-Screen to predict bacteriuria from urine specimens held at room temperature

Abstract

Results from the Bac-T-Screen (BTS) of fresh urine specimens were compared with the BTS results obtained when the same urine specimens had been held at room temperature for 24 h. Of the 246 specimens studied, 43 were initially BTS positive, 11 were false-negative, and 39 had greater than or equal to 10(5) CFU/ml. After 24 h at room temperature an additional 60 specimens had greater than or equal to 10(5) CFU/ml, of which only 16 were BTS positive; 10 specimens still gave false-negative results, and the number of false-positive specimens increased by only 6.5% of all specimens. For significant specimens (containing greater than or equal to 10(5) CFU of probable pathogens per ml), the predictive value of a negative test changed by only 0.1% (99.5 to 99.4%), whereas the sensitivity of the test remained at 96.4% for incubated specimens. Of those specimens that developed greater than or equal to 10(5) CFU/ml in vitro, 85% contained gram-negative bacilli. Neither bacteria grown in vitro nor urine specimens from normal females containing greater than or equal to 10(5) CFU/ml were positive with the BTS. For reasons not entirely understood, the BTS system may be unique in its ability to discriminate between bacteria which represent true bacteriuria and those which are present because of contamination, possibly due to other cellular elements present in infection-related bacteriuria, namely leukocytes and sloughed bladder epithelial cells.