Utilizing Digital Imaging to Determine Optimal Incubation Times for Routine Urine Cultures

Abstract

Background

Full laboratory automation has the potential to image cultures at defined period times to expedite the release of results while maximizing efficient use of laboratory staff. This study focused on TAT for urine culture results using Copan’s WASPLab digital imaging to determine optimal reading times. We compared reading urine cultures from Blood and MacConkey agars every 2 hours starting at 11/12/13 hours and up to 23/24 hours using the WASPLab.

Materials and Methods

Urine specimens collected during the fall and winter months of 2017 were included in the study. A total of 946 specimens were analyzed by observing digital images taken with the WASPLab every two hours. A total of 184 (19.5%) of the specimens were negative throughout the study period.

Results

Of the remaining 762 positive cultures, 109 (14.3%) had optimal growth at 11/12 hours of incubation, 133 (17.5%) after 13/14 hours, 84 (11.0%) after 15/16 hours, 412 (54.1%) after 17/18 hours, 10 (1.3%) after 19/20 hours and 14 (1.8%) after 23/24 hours of incubation. Thus, 31.8% of all positive urine cultures could be read optimally at 14 hours of incubation, with a total of 96.9% of all positive urine cultures having optimal reading times at or before 18 hours. In addition, all 24 urine specimens showing optimal growth after 18 hours of incubation had growth detected on blood agar on or before 18 hours. As there was a concern for possibly missing slower growing organisms after only 18 hours of incubation, such as yeast and alpha-hemolytic colonies, these cultures were looked at individually. All specimens that contained yeast (25 cultures) or small alpha-hemolytic colonies (27 cultures) were also detected at or before 18 hours of incubation.

Conclusions

In summary, based on our patient population, including reading times at 14 and 18 hours, would allow for approximately 1/3 of positive urine cultures to be worked up after only 14 hours of incubation (including over half of the cultures that contained gram negative bacilli) and the other approximately 2/3 of positive urine cultures to be worked up after 18 hours of incubation. The 3.1% of cultures that had optimal reading times after 18 hours would not be missed as growth was detected at or before 18 hours of incubation. Instituting a single 18 hour read time would allow a more optimized work flow in the laboratory, better utilization of microbiology staff, and have a positive impact to clinicians and patients.