Rapid screening for bacteriuria by light scatter photometry (Autobac): a collaborative study

A total of 2,720 urine specimens from three laboratories were evaluated by Autobac (Pfizer Diagnostics) and were compared with simultaneous colony counts for evidence of bacteriuria. Of 599 specimens with a colony count of greater than or equal to 10(5) colony-forming units per ml, 93.8% were detected within 6 h. This detection rate increased to 97% of 447 positive urine specimens when only specimens from patients not on antimicrobials were evaluated. The majority (77.9%) of positive specimens were detected as early as 3 h. Those specimens with greater than or equal to 10(5) colony-forming units per ml, which were negative by Autobac at 6 h, included organisms which are frequently considered to be contaminants (diphtheroids, lactobacilli, alpha and gamma streptococci, yeasts, and Staphylococcus epidermidis), or were from patients who were being treated with antimicrobial agents. Of 2,121 urine specimens with colony counts of less than 10(5), 98.1% were correctly determined to be negative by Autobac at 3 h. This percentage decreased to 86.0 at 6 h. The majority of these false-positive specimens were those with colony counts of 10(4) to 10(5) colony-forming units per ml. There appeared to be no major difference in results from the three laboratories or among the four lots of broth used in this study.