Urinary Dipstick Screening No Help When Patients Don't Have Pain

From Reuters Health Information

NEW YORK (Reuters Health) Apr 14 - Urinary dipstick and microscopy testing are not good at finding urinary tract infection when pain is not one of the symptoms, UK researchers report in the May issue of The Journal of Urology.

If international guidelines that recommend dipstick screening are followed, "many patients with urinary tract infection will go undiagnosed, which is no small matter given the prevalence of lower urinary tract symptoms," they said.

Last month, a separate team of researchers reported that urine dipsticks were ineffective in screening children for kidney disease. (See Reuters Health story of March 15, 2010.)

"I think that we must acknowledge serious deficiencies in our standard methods for screening out urinary infection," Dr. James Malone-Lee, senior author of the current study, told Reuters Health by e-mail.

Dr. Malone-Lee, of University College London, and colleagues obtained mid-stream urine samples from 508 patients and catheter urine samples from another 470 patients. These patients had symptoms such as frequency ("overactive bladder") or incontinence, but none of them had pain or urgency.

Using the patients' urine plus midstream samples from 42 healthy volunteers, the researchers compared leukocyte esterase, nitrite dipstick, and urine microscopy with routine urine culture (seeking 100,000 colony-forming units per mL).

Compared to standard culture of midstream urine, sensitivity and specificity, respectively, were 56% and 66% with leukocyte esterase, 10% and 99% with nitrite dipsticks, and 56% and 72% with microscopy.

In catheter specimens, sensitivity and specificity, respectively, were 59% and 84% with leukocyte esterase, 20% and 79% with dipsticks, and 66% and 73% with microscopy.

With standard culture, 15% of catheter specimens were positive. The proportion of positive cultures rose to 29% when the researchers used an enhanced culture method that could detect as few as 100 colony-forming units per mL.

The authors point out several "matters of considerable concern." For one thing, they say, the difference between the midstream and catheter urine data suggests the midstream samples were contaminated, which would mean the test results are unreliable.

Also, the fact that the rate of positive cultures nearly doubled with the more sensitive culture raises concerns over the accuracy of routine culture at 100,000 colony-forming units per mL.

Finally, they point out, nearly half of patients with overactive bladder had positive urine tests, which "indicates the need for closer scrutiny of the etiology" of this condition.

Based on these and other considerations, the investigators call for the establishment of "valid, evidence-based criteria for diagnosing urinary tract infections in patients with lower urinary tract symptoms."

Summing up, Dr. Malone-Lee added, "My practice has changed so that I pay greatest attention to the patients' symptoms, what they think is going on, and variations under treatment."

"I admit to a lifelong skepticism about the supremacy of technology over the ability of the human to reveal the nature of disease, if given the opportunity," he concluded.

J Urol 2010;183:1843-1847.