Microscopic blood in urine unreliable indicator of urinary tract cancer

Microscopic amounts of blood in urine have been considered a risk factor for urinary tract malignant tumors. However, only a small proportion of patients referred for investigation are subsequently found to have cancer.

A new Kaiser Permanente Southern California study published in the February Mayo Clinic Proceedings reports on the development and testing of a Hematuria Risk Index to predict cancer risk. This could potentially lead to significant reductions in the number of unnecessary evaluations.

Individuals with microscopic hematuria (three or more red blood cells per high-power field on a recent urine analysis) are currently referred for follow-up radiologic and invasive examinations, even when they are asymptomatic. American Urological Association (AUA) best practice policy recommendations include urine testing and abdominal computed tomography (CT) or intravenous pyelography plus renal ultrasonography. Patients may also undergo cystoscopy, a procedure that involves passing a narrow tube fitted with a miniature camera into the bladder to closely examine both the bladder and urethra.

In an earlier study, researchers had found that the AUA practice recommendations did not perform well in identifying which patients were most likely to have malignant tumors, suggesting that there might be alternative criteria that better identify patients who truly require further evaluation. Subsequently the team of investigators conducted a prospective cohort study of patients over a two-year period in an integrated care organization in three regions along the West Coast of the United States. They identified both a test cohort and a validation cohort of patients with hematuria evaluations and followed the patients passively through their electronic health records for a diagnosis of urothelial or renal cancer. The degree of microscopic hematuria, history of gross hematuria, smoking history, age, race, imaging findings, and cystoscopy findings were evaluated as risk factors for malignant tumors.

The test cohort consisted of 2630 patients, of whom 55 (2.1%) had a neoplasm detected and 50 (1.9%) had a pathologically confirmed urinary tract cancer. The strongest predictors of cancer were age of 50 years or older and a recent diagnosis of gross hematuria. Male sex was also predictive of cancer, whereas smoking history and 25 or more red blood cells per high-power field on a recent urinalysis were not statistically significant.

The findings were used to create a Hematuria Risk Index to predict cancer risk and performed comparably in the validation cohort of 1784 patients. Overall, 32% of the population was identified as low risk and 0.2% had a cancer detected; 14% of the population was identified as high risk, of whom 11.1% had a cancer found.

“These data confirm that a large number of follow-up examinations could be safely avoided,” observes senior investigator Steven J. Jacobsen, MD, PhD, Kaiser Permanente Southern California, Pasadena, California. “They suggest that microscopic hematuria is an unreliable indicator of urinary tract malignant tumors. 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. These findings may be used to simplify referral guidelines for evaluation in asymptomatic patients with microscopic hematuria and reduce the number of unnecessary evaluations.”