Urine reflex testing.

Q Please advise regarding reflex testing in urinalysis. Our present methodology calls for a microscopic if any of the dipstick chemistry is positive and if the color is not clear. This results in 60% to 70% of microscopic to be performed. If glucose or ketone or bile is positive, can microscopic not be performed?

A For several years, our institution performed microscopic urinary sediment examinations only on urine specimens with abnormal reagent-strip (dipstick) tests for protein, blood, leukocyte esterase, nitrite, glucose, bilirubin, or specimens with unusual appearance to include unusual color or any lack of clarity. Repeated studies of urinary findings in routine urinalysis by our laboratory showed a very good correlation between reagent-strip results (and physical properties) and the urine sediment findings.

An unpublished study of 800 specimens collected from outpatients at the University of Minnesota outpatient clinics showed 42% of patient specimens had correlating abnormal results, while 55% had correlating negative results. Of the remaining 3%, positive sediment findings of hyaline casts, a rare granular cast, bacteria, or a few PMNs (polymorphonuclear leukocytes) were found with negative reagent-strip results. Patient-chart examination of these exceptions indicated no urinary-tract disease.

At a later date, in-house studies showed that the presence of a positive reagent-strip test for glucose or bilirubin did not require a microscopic examination of the urine.

In summary, a request for a routine urinalysis results in a physical examination and a chemical screen with a multiple reagent strip. The microscopic analysis is performed (as a reflex test) when any of the following show a positive result:

* any abnormal color or any lack of clarity;

* protein;

* blood;

* leukocyte esterase; and

* nitrite.

Specimens with a pH greater than 8.0 or a refractometer specific gravity greater than 1.035 are also examined for sediment abnormalities. Microscopic examinations of the urine sediment are available regardless of the physical and chemical screen, if so requested by the physician.

Since the introduction of the IRIS Urinalysis 500 Workstation in our clinical laboratory at the Fairview University of Minnesota Medical Center, the microscopic examination is performed and reported on all urine specimens regardless of the chemical screen.

--Karen M. Ringsrud, MT(ASCP)

Assistant Professor

Department of Laboratory Medicine and Pathology

University of Minnesota Medical School 

Minneapolis, MN

Daniel M. Baer, MD, is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLO's editorial advisory board.

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