Microscopic Hematuria May Be Poor Predictor of Cancer

Barbara Boughton

January 10, 2013

Asymptomatic microscopic hematuria is an unreliable predictor of urothelial or renal malignancy, according to a Kaiser Permanente study of 2630 patients. The study was published online January 9, 2013, in Mayo Clinic Proceedings.

The researchers, led by Ronald K. Loo, MD, from the Southern California Permanente Medical Group in Los Angeles, found that only 1.9% of 2630 patients referred for further testing after a diagnosis of asymptomatic microscopic hematuria had a pathologically confirmed bladder or renal cancer. The patients were drawn from those with asymptomatic microscopic hematuria at Kaiser Permanent Southern California from 2009 to 2011 and were followed up through their electronic health records for a diagnosis of urothelial or renal cancer.

The study suggests that routine testing for malignancy in patients with asymptomatic microscopic hematuria may be unnecessary and may expose patients to unnecessary risks, the authors write.

The American Urological Association recommends urine testing, imaging, computed tomography scans, or intravenous pyelogram plus renal ultrasound and cystoscopy for patients aged 35 years or older with "3 or more red blood cells per high power field (rbc/hpf) on two of three properly collected urinalyses, or any high-grade hematuria (>50 rbc/hpf) or gross hematuria." The risks of such procedures include exposure to radiation and infection.

Although microscopic hematuria has long been considered a risk factor for urinary tract cancer, the prevalence of urinary tract cancer has been reported to be low in previous studies, at between .43% and 13%. In the Kaiser Permanente study, the authors found that age over 50 years and gross hematuria were the most reliable predictors of urothelial or renal cancer. Their analysis also indicated that microscopic hematuria was not a good predictor of cancer risk, although high-grade hematuria was a clear risk factor. Male sex and smoking history were also predictive of cancer, the researchers said.

Hematuria Risk Index

Using a validation cohort of 1784 patients with asymptomatic microscopic hematuria, also selected from Kaiser Permanente in southern California, the researchers developed a tool to predict the risk for bladder or renal cancer. Their Hematuria Risk Index used age and gross hematuria as the strongest predictors of cancer but also factored in other risk factors such as smoking history, degree of hematuria, and male sex. Patients were classified as being at low, moderate, or high risk for renal or bladder cancer.

In the validation cohort, the overall rate of pathologically confirmed bladder or renal cancer was 3.4%. Using the Hematuria Risk Index, the authors identified 32% of the validation cohort as low risk for urinary tract cancer, and results indicated that 0.2% of these patients were actually diagnosed with cancer. In the 14% of patients identified as high risk by the index, 11.1% had a cancer detected.

The Hematuria Risk Index overall proved to be a reliable indicator of malignancy, as indicated by the area under the receiver operating characteristic curve (AUC). The AUC scale ranges from 0.5 to 1, with 1 indicating the most reliability. The Kaiser Permanente Hematuria risk index had an AUC of .829.

The study's strengths include the large number of patients evaluated and the fact that they were drawn from a diverse real-world healthcare setting, the authors note. However, the study was limited by the differences between the test and validation cohort, the researchers add. Patients in the test cohort were younger, and more were women, than in the validation cohort. In addition, in the validation cohort, twice as many patients had a history of gross hematuria than in the test cohort.

Still, the study indicates that guidelines for testing of patients with asymptomatic microscopic hematuria need to be simplified and changed to reduce the number of unnecessary and invasive tests, the researchers conclude.

"Patients with microscopic hematuria under the age of 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," they conclude.

The study was funded by Kaiser Permanente Southern California. The authors have disclosed no relevant financial relationships.

Mayo Clinic Proc. Published online January 9, 2013.