Screening for Significant Bacteriuria in Patients with Upper Tract Calculi Using Dipstick Urine Analysis

Abstract

Following extracorporeal short-wave lithotripsy (ESWL), urinary tract infection (UTI) and bacteremia may develop, owing to the release of bacteria from infected calculi and the associated parenchymal trauma.1,2 However, it would appear that in those patients with sterile urine or insignificant bacteriuria defined as less than 10 4 cfu/mL in pure growth and less than 5 WBC per high-power field, antibiotic prophylaxis is unjustified.3-7 While this makes good sense, the problem remains as to how to identify those patients with infected urine at the time of treatment. Laboratory assessment of microscopy, and semiquantitative culture is time consuming. Results may take up to 48 hours to obtain, by which time, patients are back in the community and further delaying the commencement of antibiotic therapy.Laboratory assessment is not only time consuming but also costly. In order to circumvent this, many authors have investigated the use of other methods for the detection of bacterial infection, using less direct methods that allow identification of those patients in whom laboratory analyses are likely to prove useful. Use of reagent strips that detect protein, blood, nitrite and leukocyte esterase have proven useful in a number of clinical settings. [8][9][10][11][12] This retrospective study evaluates the accuracy of dipstick testing compared with routine laboratory analysis in detecting significant bacteriuria, as defined above in patients undergoing ESWL. Materials and MethodsWe evaluated a total of 270 midstream urine (MSU) samples from 165 patients (mean age 57.4 years; male to female ratio 4:1) attending the King Fahd Armed Forces Hospital Stone Unit for ESWL. Fifteen patients (20 samples) attending for treatment during this period and already receiving antibiotic therapy or with clinical UTI, were excluded from the study. MSU samples were taken on admission and transported promptly to the laboratory for microscopy, culture and sensitivity. Reagent StripsMultistix-8SG strips (Ames Division, Miles Laboratory Ltd) provide reagent tests for the determination of pH, protein, ketones, blood, nitrite and leukocyte esterase. We limited our observations to results for protein, nitrite, blood and leukocyte esterase. The nitrite test is dependent upon the conversion of nitrate to nitrite by nitrate reductase, an enzyme produced predominantly by gram-negative bacteria. A positive leukocyte esterase test depends upon the presence of esterase from granulocytic leukocytes. For each sample, a Multistix-8SG reagent strip was dipped into fresh well-mixed urine. The strips were read photometrically by the Clinitek 100 reflectance photometer (Ames Division, Miles Laboratory Ltd). Test results were automatically recorded on a built-in thermal printer. For the purpose of this study, the reagent strips were regarded as positive if one or more strips demonstrated a positive result. Trace results were regarded as negative. CultureAll MSU specimens were sent for routine laboratory microscopy, culture and sensitivity after reagent strip te...