Fast and accurate prediction of positive and negative urine cultures by flow cytometry.

BACKGROUND: Urinary tract infection (UTI) is a widespread infectious disease in humans. Urine culture, a huge workload in the microbiology laboratory, is still the standard diagnostic test for UTI, but most of the cultures are negative. A reliable screening method could reduce unnecessary cultures and quicken reporting of negative results. METHODS: We evaluated the usefulness of a flow cytometry (FC) screening method in the prediction of positive urine culture to reduce the number of urine cultures. The urine specimens sent to the laboratory for culture were tested with the flow cytometer Accuri C6. FC bacterial counts were compared to standard urine culture results to assess the best cut-off values. RESULTS: Two hundred nine urine samples were included, of which 79 (37.8 %) were culture positive. On comparing the culture and the FC data in the ROC curve, the FC bacterial counts of ≥10(6) bacteria/mL provided a reliable screening for bacteriuria with a sensitivity and specificity of 99 and 58 %, respectively. All negative FC results (<10(6) bacteria/mL) showed a negative predictive value of 99 % with a negative likelihood ratio of 0.02. The FC bacterial counts of ≥10(8)/mL showed a positive predictive value of 99 % with a positive likelihood ratio of 60.9. CONCLUSIONS: Counting bacteria in human urine samples by the FC is a fast, accurate and cost-effective screening method for bacteriuria. Our results showed that FC is able to rule out UTI, which can lead to a substantial reduction (36 %) of urine cultures. It also demonstrated that this method predicts positive cultures accurately.

Accurate and fast urinalysis in febrile patients by flow cytometry.

BACKGROUND: The urine culture is worldwide accepted as the gold standard in diagnosing urinary tract infections, but is time consuming and costly, other methods are fast but moderately reliable. We investigated whether counting the number of bacteria by flow cytometry could be a fast and accurate method to analyze urine samples in febrile patients at the emergency department (ED). METHODS: Urine samples were obtained from 140 febrile patients at the ED. Urinalysis was performed according to standard procedures. Flow cytometric analysis for bacteria was performed with the Accuri C6 flow cytometer. Diagnostic values were determined at various cut-off points by using urine culture as the gold standard. RESULTS: The highest diagnostic accuracy of urinalysis of bacteria was obtained with flow cytometric analysis (AUC of 0.96). The best cut-off value for bacteria counted by flow cytometry based on the ROC-curve was 3.72 × 106 bacteria/mL, this resulted in a sensitivity of 94.7% and a specificity of 88.2%. CONCLUSIONS: Counting bacteria by flow cytometry has the highest diagnostic accuracy and is superior to other methods in urinalysis in febrile patients in the ED when using urine culture as the gold standard.