Clinical Laboratory Practices in Speciating Organisms and Reporting Results of Voided Urine Cultures
Studies comparing midstream voided and catheter urine specimens in symptomatic women have shown that colony counts of E. coli as low as 102CFU/mL in midstream voided urine (MSU), even when in mixed growth, are predictive of bladder infection. Given that clinical laboratories generally do not quantify organisms in MSU cultures to this level, the use of MSU cultures in the diagnosis of cystitis may lead to inappropriate interpretation of culture results. We queried laboratories to ask about their MSU culture and reporting practices.
A convenience sample of clinical microbiology laboratories in Miami, Florida, and nationally were queried. We called the laboratories to ask the microbiology laboratory manager and/or the clinical microbiologist about their practices in speciating and reporting results of MSU cultures and to send us any written algorithms relevant to such practices.
We queried 11 local and 3 national clinical microbiology laboratories for our study. We were able to talk by telephone with laboratory personnel in all 14 laboratories to obtain study information, but only 8 laboratories sent us their MSU culture algorithms. No laboratory refused to provide us with information. Results are shown in the Table.
Table: Species identification and reporting of organisms growing in MSU.
No. organisms grown and colony counts
No. (%) of labs speciating and reporting
≥ 3 organisms at any colony count
≤ 2 organisms, CFU/mL for either or both
*9 laboratories report such cultures as “mixed flora”, 3 “contaminated urine” and 2 “multiple organisms present”; 5 of 14 also suggest to repeat the specimen
†4 other laboratories report growth at 103- <104 CFU/mL but don’t speciate; 9 report as “no growth”
‡9 report “no growth”; 5 report “<103 CFU/mL of unidentified organism”
Only one of 14 clinical microbiology laboratories speciate and report organisms in MSU if ≤2 organisms grow at 103-<104 CFU/mL, and none do if ≥ 3 organisms grow at any colony count. Lack of awareness by clinicians as to how their clinical microbiology laboratory reports MSU results may result in misinterpretation of such results, including underdiagnosis of low colony count or mixed growth E. coli UTIs.