The presence of microscopic levels of blood in the urine is unreliable as an indicator for renal or bladder cancer, report researchers.
"An extremely small proportion of patients with microscopic hematuria are subsequently found to have cancer," say Steven Jacobsen (Kaiser Permanente Southern California, Pasadena, USA) and team.
This suggests that many of the follow-up examinations of patients with asymptomatic microscopic hematuria, which often include radiologic and invasive procedures, are unnecessary and can safely be avoided, they say.
Currently, the American Urological Association recommends a thorough urologic evaluation of all asymptomatic patients aged 35 years or older who have a single analysis result with three or more red blood cells per high-power field (RBC/HPF).
Instead, Jacobsen and colleagues recommend that a history of gross hematuria (>50 RBC/HPF [when blood is present at levels visible in urine]) is a far more reliable indicator of the need for such patient follow up.
As reported in Mayo Clinic Proceedings, the team found that, of 2630 patients who underwent full evaluation for asymptomatic microscopic hematuria between January 2009 and October 2010, only 50 individuals were found to have malignant tumors, giving an overall cancer detection rate of 1.9%.
Five risk factors were associated with pathologically confirmed cancer, namely male gender, age of 50 years or older, a history of gross hematuria (>50 RBC/HPF), smoking history, and at least 25 RBC/HPF on a recent urine analysis.
However, in multivariate analysis only history of gross hematuria, age ≥50 years, and male gender were significantly associated with risk for cancer diagnosis, at odds ratios of 9.9, 16.3, and 2.5, respectively.
The researchers used this information to create a "Hematuria Risk Index" in which history of gross hematuria and age ≥50 years were awarded 4 points and the remaining three risk factors awarded 1 point each, giving index score groups that could be used to identify patients as at low (0-4 points), medium (5-8), or high risk (9-11) for a cancer diagnosis. The area under the receiving operating characteristic curve (AUC) for the risk index was 0.809.
When the team applied this risk tool to a validation cohort of 1784 patients, the predictive ability was higher than in the original cohort, at an AUC of 0.829. Among 32% of individuals who were identified as low risk, only 0.2% had an actual diagnosis of cancer whereas, among 14% of the cohort who were classified as high risk, 11.1% had a cancer diagnosis.
"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," say Jacobsen et al.
"These findings may be used to simplify referral guidelines for evaluation of asymptomatic patients and microscopic hematuria and reduce the number of unnecessary evaluations," they conclude.
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