Urine dipstick is 91% to 100% sensitive and 65% to 99% specific for the detection of microscopic hematuria greater than three RBCs per high-power field. False-positives occur with myoglobin, hemoglobin and iodine. Red cell casts, dysmorphic cells and significant proteinuria indicate a glomerular source.
The American Urological Association definition of microscopic hematuria is three or more red blood cells per high-power field on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens. The cause of hematuria is found in 85% of patients. Up to 26% of patients with microhematuria are discovered to have genitourinary malignancies, depending on the population evaluated although the number of all comers is much lower at 5-10%. 92% of cancers discovered on work-up for microhematuria were diagnosed while still localized and curable. High-risk patients, cigarette use and those with occupational exposure or history of chronic phenacetin use, should be considered for full urologic evaluation. Intravenous urography, ultrasonography and computed tomography are used to evaluate the urinary tract in patients with microscopic hematuria. Cystoscopic and cytology are also used. An initial negative work up may have to be followed with yearly screening in high risk patients.
- Patients with hematuria associated with a UTI should have a repeat urinalysis in 6 weeks
- Hematuria in a patient over 40 years of age represents a malignancy until proved otherwise
- Anticoagulation alone does not commonly induce hematuria de novo
As emergency physicians we send a lot of urine. Referral for microscopic hematuria, especially for high risk and patients over forty, is an important part of complete medical care.
Yun, et al. Evaluation of the patient with hematuria. Medical Clinics of North America – Volume 88, Issue 2 (March 2004)
Grossfeld, et al. Asymptomatic Microscopic Hematuria in Adults: Summary of the AUA Best Practice Policy Recommendations. American Family Physician – Volume 63, Issue 6 (March 2001)