Urine dipsticks, microscopy and enhanced urinalysis have been used in an attempt to improve the speed at which a diagnosis of urinary tract infection (UTI) is reached; however, these methods have not been 100 percent sensitive. Missing the diagnosis or delaying treatment of a UTI may be associated with renal damage. Bulloch and colleagues conducted a study to determine whether a visual inspection of urine clarity is predictive of UTI.
Patients younger than 21 years who presented to the emergency department were eligible for the study if a midstream clean-catch or catheterized urine sample was collected. Patients who were referred for a positive urine culture or for an abnormal urine test were excluded, as were patients with a history of underlying renal or genitourinary problems and those who were taking antibiotics. A sample of urine consisting of 3 mL was poured into a standard blood-collection tube and held 1 cm from a white background paper covered with standard 11-point font print and viewed under normal fluorescent lights. The observer compared the clarity of the text through the urine sample with the text seen through an identical test tube filled with water. If the text was seen to be the same through both test tubes, the urine sample was considered clear. A second observer performed the same test. If there was a discrepancy between the two opinions, the specimen was considered to be cloudy. Unclear urine was treated with an acetic acid solution to dissolve phosphates that could be clouding the urine. Clinical symptoms and results of the urinalysis were recorded (see accompanying table).
Of the 159 samples collected, 70 (44 percent) were catheterized specimens and 89 (56 percent) were midstream clean-catch specimens. Of the 51 children younger than two years, 49 specimens (96 percent) were obtained by catheterization. Forty-nine urine specimens (31 percent) were determined by the observers to be cloudy. Acetic acid did not result in clearing any of the cloudy specimens. Urine cultures were positive in 29 of the samples (18 percent prevalence). Of the 130 negative cultures, 107 were clear on visual inspection (specificity: 82.3 percent). There were 110 visually clear specimens; 107 of these were negative cultures (negative predictive value: 97.3 percent). Three patients had clear urine and a UTI. All three of these patients had a negative result on urine dipstick. On microscopy, two of the three patients had less than five white blood cells per high-power field and some bacteriuria; the third patient had more than 15 white blood cells per high power field and a large amount of bacteriuria.
The authors conclude that visual examination of urine is an effective bedside screen for predicting UTI in children. However, the authors state that clear urine cannot definitively rule out UTI.
|Test||Sensitivity, % (95% CI)||Specificity, % (95% CI)||Positive predictive value, % (95% CI)||Negative predictive value, % (95% CI)||Positive likelihood ratio||Negative likelihood ratio|
|Urine clarity (overall)||89.7 (72.7−97.8)||82.3 (75.7−88.9)||53.0 (38.3−67.5)||97.3 (92.2−99.4)||5.07||.13|
|Urine clarity (catheterized specimens only)||83.3 (51.6−97.9)||86.2 (74.6−93.9)||55.6 (30.8−78.5)||96.2 (86.8−99.5)||6.04||.19|
|Urine clarity (MSU only)||94.1 (71.3−99.8)||79.2 (68.0−87.8)||51.6 (33.1−69.8)||98.3 (90.8−100.0)||4.52||.07|
|LE (> small)||82.8 (64.2−94.2)||95.4 (90.2−98.3)||80.0 (61.4−92.3)||96.1 (91.2−98.7)||18.0||.18|
|Nitrite||27.6 (12.7−47.2)||97.7 (93.4−99.5)||72.7 (39.0−94.0)||85.8 (80.2−91.4)||12.0||.74|
|> 5 WBC/hpf||86.2 (68.3−96.1)||78.5 (71.4−85.5)||47.2 (33.3−61.4)||96.2 (90.6−99.0)||4.01||.18|
|Bacteria on microscopy||93.1 (77.2−99.2)||40.0 (31.6−48.4)||25.7 (17.4−34.1)||96.3 (87.2−99.5)||1.55||.17|
|> Small LE or positive nitrite (abnormal dipstick)||82.8 (64.2−94.2)||93.8 (88.2−97.3)||75.0 (56.6−88.5)||96.1 (91.0−98.7)||13.40||.18|
|> 5 WBC/hpf or bacteria on microscopy (abnormal microscopy)||100 (88.1−100)||32.3 (24.3−40.3)||24.8 (17.0−32.6)||100 (91.6−100.0)||1.48||—|
|Abnormal dipstick or abnormal microscopy||100 (88.1−100)||33.1 (25.0−41.2)||25 (17.1−32.9)||100 (91.8−100.0)||1.49||—|