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The Use of Phase Contrast Microscopy to Identify Bacteriuria and Hence Predict Cultures Indicative of Urinary Tract Infections



Objective: To determine whether phase contrast microscopy of uncentrifuged urine specimens could rapidly and accurately identify bacteriuria and predict microbiology culture results.

Methods: A prospective study was performed at the Clinical Microbiology Laboratory of the EWMSC, Trinidad. Urine samples were examined via phase contrast microscopy at the time of culture.

A sample size of 187 was based on the availability of the clinician to get to the laboratory at the time of urine culture. Uncentrifuged, unstained urine samples were examined with microscopes enabled with phase contrast at 400x magnification mounted on a Hawksley Nebauler counting chamber. Samples were interpreted as being either “Positive,” “Negative” or “Indeterminate” based on their level of bacteriuria. “Indeterminate” specimens were not further analysed.    

Results: One hundred and ninety-three samples were microscoped. Immediate determination was made for 187 samples (96.9%). Six samples were deemed as “Indeterminate.” Of the 187 microscopy interpretations, only 30 showed discordance between the microscopy and culture results. Sensitivity of 47/54 (87%), specificity 110/133 (82.7%), positive predictive value 47/70 (67.1%) and negative predictive values of 110/117 (94%) were obtained.

Conclusions: Phase contrast microscopy afforded immediate interpretation in 187/193 (96.9%) of samples studied. Microscopy interpretation showed high sensitivity, specificity, positive and negative predictive values when compared to the accepted gold standard i.e., microbiological culture. 

13 Nov, 2017
e-Published: 15 Nov, 2017


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