Asymptomatic microscopic hematuria is an unreliable indicator of urinary cancers, suggesting that many patients could avoid radiologic and invasive follow-up examinations, according to researchers.

In a prospective study, a team led by Steven J. Jacobsen, MD, PhD, of Kaiser Permanente Southern California in Pasadena, found that the presence 25 or more red blood cells per high-power field (RBC/HPF) on a recent urinalysis and history of smoking were not significantly associated with a subsequent diagnosis of bladder or kidney cancer.

The researchers enrolled a test cohort of 2,630 patients, of whom 55 (2.1%) had a neoplasm detected and 50 (1.9%) had a pathologically confirmed urinary cancer. In this group, age of 50 years or older and a recent diagnosis of gross hematuria were the strongest predictors of cancer, the investigators reported online in Mayo Clinic Proceedings. The study found that male gender also predicted cancer.

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Dr. Jacobsen’s group used these factors to develop a Hematuria Risk Index, which they tested in a validation cohort of 1,784 patients. In this index, factors associated with a higher risk of bladder or kidney cancer (age 50 years and older and a history of gross hematuria) were assigned four points, whereas history of smoking, male gender, and 25 or more RBC/HPF on a recent urinalysis were assigned one point. Thus, the index can range from 0-11 points. Patients with a score of 0-4 points were considered to be a low risk for urinary cancer, whereas those with a score of 5-8 and 9-11 points were classified as being at moderate and high risk, respectively.

Overall, 32% of the validation cohort was identified as low risk, and only 0.2% had a cancer detected; 14% were identified as high risk, and 11.1% of them had cancer found.

“Patients with microscopic hematuria younger than 50 years and with no history of gross hematuria may not benefit from further evaluation and therefore could avoid unnecessary risk from radiation exposure and invasive endoscopy,” the researchers concluded.