Adeel Gardezi, Sajjad Hussain Mirza, Umar Khursheed, Muhammad Farooque, Amin Waqar.
Microscopy of Gram stained uncentrifuged drop of urine for presumptive diagnosis of urinary tract infections.
Pak J Pathol Jan ;17(3):111-4.

Objective: To evaluate the diagnostic efficiency of microscopic examination of Gram stained uncentrifuged drop of urine for presumptive diagnosis of urinary tract infections (UTI). Methods: 250 samples collected from March 2005 to August 2005 comprising of both in patient and out patient samples were analyzed. Urine sample was homogenized and a nickel-chrome loop, calibrated to 10µl was used to take a drop of urine and was applied on glass slide (25mm x 75mm). The drop was allowed to dry in air at room temperature (25° C approx.) without spreading. The slides after drying were stained with Gram method of staining. The microscopic examination was carried out with a 100x oil immersion objective, 30 fields were examined. Observation of one or more microorganism per high power oil immersion lens was taken as a positive reading. Culture of urine was taken as reference method and performed by using filter paper strips applying 2µl of urine on cystine-lactose-electrolyte-deficient agar. Culture results obtaining a mixed growth of =2 organisms were excluded out of the study. Only those cultures were taken as positive and made part of the study which yielded more than 105 or 104 to 105 CFU of pure single type /ml of urine. Sensitivity, specificity, positive and negative predictive values were calculated by using appropriate formulas. Results: A total of 250 samples were processed for the study. Out of which 39 (15.6%) samples yielded mixed growth of =2 organisms. All these samples were excluded out of the study (remaining 211 samples). Microscopic examination of 97(45.9%) samples showed no organism and no growth was obtained on subsequent culture of these samples (true negative). 61 (28.9%) samples were found to have =1 organism in Gram stained smear of uncentrifuged single drop of urine and their culture yielded growth of =105 or 104 to 105 CFU of pure single type /ml of urine (true positive). No organism was detected on microscopic examination of 9 (4.2%) samples however pure growth of single organism was obtained on their culture (false negative). =1 organisms were seen on the microscopic examination of 44 (20.8%) samples which failed to grow on culture media (false positive). Sensitivity (87.1%), specificity (61.39%), positive predictive value (58.09%), negative predictive value (91.5%) was calculated by using respective formulas. Conclusion: This method provides a good negative predictive value and helps to rule out the presence of UTI efficiently when bacteria are not seen on microscopic examination. A very simple method without the use of laboratory centrifuge and culture media makes it an ideal practice in peripheral laboratories devoid of adequate resources and facilities to deal with one of the most commonly received specimens.

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