Many people have some amount of blood in their urine, but relatively few have a serious problem.
In a population-based study in Rochester, Minnesota, red blood cells were found in the urine of 13% of symptom-free adults.1 In other studies, the figure ranged from 9% to 18%.2
Hematuria is sometimes detected during investigation of symptoms such as dysuria, urinary frequency, or flank pain. However, many referrals to urologists are made purely on the basis of the results of a dipstick urinalysis screening test in a patient without symptoms.
The United States Preventive Task Force3 discourages routine testing for hematuria to screen for bladder cancer in patients without symptoms, and the Canadian Task Force on the Periodic Health Examination4 and the American Urological Association (AUA)2,5 do not recommend it either. Nevertheless, approximately 40% of primary care physicians believe in it,6 although the number seems to be declining.7 A reason that dipstick testing is so popular is that it is an inexpensive and simple way to detect glucosuria and medical renal disease.8–11
The risk of significant disease in a patient with microhematuria but without symptoms is low, and the evaluation for hematuria can be costly and invasive. For an individual patient with a hemoglobin-positive dipstick test, the finding should not be ignored, but the patient does not necessarily need a complete evaluation. It is important to determine which patients require urologic studies and consultation, nephrologic evaluation, or no intervention at all.
This review addresses issues related to hematuria for the primary care physician, clarifies some of the important definitions, builds on these terms to delineate which patients should be referred to a urologist, and provides simple recommendations about ancillary studies and their potential role before urologic consultation. Understanding this information will ultimately assure appropriate management of patients without symptoms who have positive dipstick screening tests, leading to decreased use of costly and invasive tests and more appropriate long-term follow-up.
Gross (macroscopic) hematuria is blood in the urine that is visible without microscopy. This condition almost always warrants urologic evaluation.2,5
Microscopic hematuria, or microhematuria, is the finding of red blood cells in the urine on microscopy. (In contrast, in dipstick hematuria—see below—blood cells may or may not be present in the urine.)
“Dipstick hematuria” and “dipstick microhematuria” are potential misnomers. The dip-stick test for hematuria is a nondiagnostic screening test. A positive result is simply a color change due to oxidation of a test-strip reagent; it does not confirm that blood cells are present. Factors that can cause a false-positive result on a dipstick test include hemoglobinuria, myoglobinuria, concentrated urine, menstrual blood in the urine sample, and rigorous exercise.12 Thus, the diagnosis of hematuria cannot be made by dipstick alone. Unless red blood cells are seen microscopically, the term microhematuria is inappropriate.
Of note, if the specific gravity of the urine is very low (< 1.007), microscopy can fail to detect urinary red blood cells, owing to cell lysis.2 This limitation can be overcome by restricting the patient’s fluid intake and then repeating the urinalysis.
Many patients with a positive dipstick oxidation reaction are labeled as having dip-stick hematuria although microscopic analysis would show that red blood cells are absent. Perhaps the term dipstick pseudohematuria would be more accurate. These patients will not benefit from a costly and invasive urologic workup, so it is crucial to distinguish them from patients with true microhematuria.
SIGNIFICANT HEMATURIA: ≥ 3 RBCs/HPF
Microhematuria is often intermittent, and many healthy patients occasionally have a few red blood cells in the urine.13 However, no cutoff point for the amount of hematuria can be used to rule out the possibility of cancer.14 To account for these complicating factors, the AUA Best Practice Policy Panel on Asymptomatic Hematuria considered the literature and expert opinions to define the amount of microhematuria warranting evaluation in patients with risk factors for significant urologic disease.2,5
The AUA panel defined microhematuria as an average of three or more red blood cells per high-power microscopic field (RBCs/HPF) in two out of three properly collected and prepared specimens. Urine should be collected midstream after wiping the urethral meatus with a disinfectant and voiding the initial portion of urine into the toilet. For proper preparation of the urine sample, 10 mL of urine should be centrifuged at 2,000 rpm for 5 minutes and the supernatant discarded. The sediment should then be resuspended in 0.5 to 1.0 mL of remaining urine, and a drop of this suspension should be examined microscopically. If contamination is suggested (ie, if squamous epithelial cells, bacteria, or both are present), one should consider collecting a specimen through catheterization.2,5
The AUA guidelines do not specify some of the details of management, such as the timing of subsequent microscopic urinalyses, but we recommend that all urinalyses to establish whether significant hematuria is present be done within 3 to 6 months of the screening dip-stick test. If a patient has no risk factors for cancer and has a negative result on the first microscopic urinalysis, the follow-up test can be performed in 1 year. Table 1 shows risk factors for significant urologic disease that warrant evaluation in patients with asymptomatic hematuria.5
Isolated urinary findings that might warrant evaluation by a nephrologist rather than a urologist include proteinuria, red cell casts, and dysmorphic red blood cells, especially if the serum creatinine level is elevated.2,5 Many medical renal conditions (eg, glomerulonephritis) and hemoglobinopathies (eg, sickle cell trait) can cause blood in the urine; when these conditions are accompanied by risk factors for urologic disease, urologic evaluation is indicated as well.