Pyuria Poor Sign of UTI in Stone Cases
In a prospective study of 238 emergency room patients, they examined performance characteristics of pyuria as an indicator of UTI accompanying CT-confirmed acute urolithiasis.
UTI was defined as the presence of 103-cfu/mL or greater of a single pathogen. Among the 238 patients, 67% were male. The median age was 41 years; 89% had flank pain, 58% had nausea, 41% had dysuria, 33% had hematuria, 20% reported frequency, 12% reported a history of fever, and 4% presented with fever.
The most common pathogens were Escherichia coli (44%), Staphylococcus species (16%), Proteus mirabilis (12%), viridans streptococci (12%), Group B streptococci (12%) and unspecified Gram-negative bacteria (4%).
“There is a lot of debate over this topic among clinicians, and this is the first study ever done to see how accurate urinalysis is at predicting urinary tract infections in patients presenting with acute symptomatic kidney stones,” said lead investigator Fredrick M. Abrahamian, DO, FACEP, assistant professor of medicine at the David Geffen School of Medicine at the
Antibiotics were prescribed for 44 patients (19%), even though only 27% had a microbiologically confirmed UTI. Among the 25 patients with a microbiologically confirmed UTI, fewer than half were prescribed antibiotics. Pyuria at the usual levels of 5-20 white blood cells/hpf exhibited low sensitivity for predicting UTI, with a threshold of 5 cells/hpf picking up only 52% of UTIs. The specificity of pyuria as a predictor of UTI rose with increasing urine leukocyte count threshold. Overall, the researchers concluded that pyuria exhibited only a moderate specificity at predicting UTI.
“Oftentimes, when a patient presents with kidney stones, there are some white blood cells in the urine, and that may just be due to the stone coming down the urinary tract and causing inflammation and irritation of the ureter,” explained Dr. Abrahamian, who also is director of education in the department of emergency medicine at Olive View-UCLA Medical Center in Sylmar, Calif. “So, no one really knows what white blood cells in the urine mean in patients with symptomatic kidney stones.”
He also reported, “A high degree of pyuria increased the probability of a positive culture, but it was not a highly accurate test. The sensitivity of pyuria in the setting of kidney stones was quite low. So there seems to be a need to do a further workup and not rely just on urinalysis.
“Currently,” he added, “it appears that relying exclusively on urinalysis will result in either undertreating or overtreating with antibiotics. You should add cultures and follow up on the results so you are certain what they show.”