How to evaluate ‘dipstick hematuria’: What to do before you refer

STUDIES TO CONSIDER BEFORE CONSULTATION

In symptom-free patients, it is inappropriate to order laboratory or imaging tests on the basis of a dipstick test alone, without confirming that they actually have hematuria. When the blood is confirmed to be present by microscopic examination of centrifuged urine (as described above), benign causes such as UTI should be considered. If a patient does have a UTI with hematuria, urinalysis should be repeated once the infection has cleared up.

Imaging studies

For symptomatic microhematuria. Patients with acute symptoms of renal colic should undergo computed tomography (CT) in a “stone protocol” (without contrast, with 3- to 5-mm cuts of the abdomen and pelvis) to assess for urinary lithiasis. Pregnancy should always be ruled out before radiation exposure; renal ultrasonography is generally the first-choice imaging study for pregnant patients.

For asymptomatic microhematuria. Patients without the classic flank pain of urolithiasis should undergo more extensive studies. For patients at increased risk of cancer, such as heavy smokers, CT urography is the optimal imaging study and is the test least likely to necessitate other follow-up studies.^18–20 Other imaging options, including ultrasonography and intravenous pyelography, incompletely assess the upper urinary tracts including both renal parenchyma and urothelial surfaces. CT urography has been shown to find more than 40% of hematuria-causing lesions missed by other studies.¹⁸ Because ordering alternative imaging first will often result in redundant studies, CT urography is the preferred initial imaging study in the evaluation of hematuria.

Before exposing a patient to contrast media, one should ascertain that he or she is not allergic to it. In addition, in patients at risk of contrast nephropathy (ie, those older than 60 years, with diabetes, or with preexisting medical renal disease), one should check the serum creatinine concentration. Magnetic resonance urography, a more expensive study, is as accurate as CT for diagnosing many urologic conditions, so it can be performed in lieu of CT urography in patients with renal insufficiency, iodine allergy, or any reason to avoid ionizing radiation. Some clinicians perform plain radiography of the kidneys, ureters, and bladder as well as ultrasonography in this setting, but determination of the appropriate alternative to CT urography, if required, is best left to the urologist.

Other tests

Cytologic testing of the urine can be valuable in patients with gross hematuria and in those with microhematuria who have risk factors for urinary tract cancer. Although its reported median sensitivity for malignancy is only 48%, a positive cytologic test is approximately 94% specific for malignancy.²¹ Other studies, such as the fluorescence in situ hybridization assay, and the nuclear matrix protein 22 test do not yet have a clear role in the diagnosis of urinary tract disease.²²

However, in general, we caution non-urologists not to order special tumor marker or cytologic tests, or to do so only with careful forethought. Although these studies occasionally detect occult cancer in patients at high risk, an “atypical” finding on cytology or a positive tumor marker test can lead to inappropriate referral and unnecessary biopsy or other tests.

WHEN NOT TO REFER A PATIENT WITH HEMATURIA TO A UROLOGIST

Symptom-free patients with a positive dipstick hemoglobin test should not immediately be referred to a urologist: they should have a microscopic urinalysis first to determine whether they actually have microhematuria, unless microscopic laboratory services are unavailable. Only patients with documented true hematuria, as defined by the AUA guidelines, should be referred for urologic evaluation and diagnostic testing. Once a patient is referred for evaluation, the consultant is under clear pressure to perform a complete investigation to fulfill the expectations of the referring physician. Avoiding expensive unnecessary testing and referral in those without hematuria allows appropriate utilization of resources.

Patients with microhematuria associated with a UTI should have a repeat urinalysis after the UTI is successfully treated; if the hematuria clears with the infection, then the patient needs no further evaluation. Patients with dipstick pseudohematuria and significant proteinuria or a predominance of dysmorphic urinary blood cells might benefit from an evaluation by a nephrologist rather than a urologist.² This is especially true if the patient has an elevated serum creatinine level.

ECONOMIC RELEVANCE

In our tertiary care urology clinic, approximately 75% of patients who are referred to us because of microhematuria have not had a microscopic urinalysis before coming here. On further evaluation, up to 75% of these patients are found to have dipstick pseudohematuria that did not actually require consultation or evaluation.²³ It is possible that this occurs even more frequently in the general practice setting.

A Medicare level-4 urologic consultation for hematuria costs $170; the cumulative cost of unwarranted referrals is undoubtedly substantial. Even more money is wasted on CT urography, cytology, and other testing performed before urologic consultation in patients ultimately found not to have true hematuria. The economic and iatrogenic risks of evaluation cannot be justified in patients who do not exhibit findings that can be considered abnormal as defined in this article.

CONCLUSION

It is important to distinguish whether hematuria is microscopic or macroscopic, whether there are associated symptoms, and whether a patient has risk factors for significant urologic disease. While dipstick tests are sensitive, they do not reliably diagnose microhematuria, which is the microscopically proven presence of urinary red blood cells. Positive dipstick tests should always be followed by microscopic urinalysis; failure to do so can result in the unfortunate and unnecessary evaluation of dipstick pseudohematuria, a normal condition.

The AUA defines significant hematuria as three or more RBCs/HPF in two of three properly prepared specimens.² This should determine whether a symptom-free patient needs urologic referral and evaluation for hematuria.

By following these principles, primary care physicians have a valuable opportunity to direct medical care, increase the efficiency of our health care system, and protect patients from the anxiety, costs, and risks of an unnecessary urologic workup.