Editor’s note: Not long ago MLO received a question from a reader in Washington state.
“I had occasion to ask fellow lab managers ‘How many of you do the following confirmatory or secondary tests for urinalysis: Clinitest, Acetest, Sulfasal or TCA, Icotest, Refractometer, other?’ I was surprised at the variety of responses, indicating a lack of standardization. Are there requirements, standards, etc. or is it truly up to the individual labs for Best Lab Practice?”
We put the question to our experts, Drs. Block and Lieske, and here is their response.
Confirmatory urinalysis tests confirm the presence of the same analyte detected with screening tests, but offer improved sensitivity and/or specificity or confirm the result via an alternate methodology.1 Some confirmatory tests may have been significant historically, but are less useful in today’s clinical practice. However, there are no standard guidelines that provide the laboratory with a definitive answer to this question. CLSI states that each lab should consult the manufacturer’s package insert for urinary dipsticks regarding interfering substances and limitations (e.g., color, protein, red cells). Table 1 (click here to view table 1 in a separate window) summarizes common screening and confirmatory methods for analytes often tested on a routine urinalysis. A second and related question regards the use of manual microscopy. Some laboratories use automated platforms exclusively (e.g., IRIS, Sysmex), while others have criteria to confirm pathologic findings detected by these instruments via reflex manual microscopy (e.g., red cell casts or renal tubalar cell casts). Another strategy is to use dipsticks as a screen with reflex manual microscopy only if an abnormality is present (e.g., proteinuria, hematuria, nitrites, or leukocyte esterase).
Taking this approach to the extreme, a regional laboratory serving 800,000 members of a health maintenance organization (HMO; Nesher, Israel) discontinued all manual microscopy reflex testing in 1999 and now performs it only upon physician request.2 In the decade since adapting this strategy the rate of manual microscopy was reduced from 17.9% of all urinalyses to 0.2% today (n=19,006 to <50 per 6 month period). There were no reported physician complaints. This is one extreme in the spectrum of options, and laboratories should decide when to perform microscopic examination of urine sediment and other confirmatory tests based on the known limitations of their screening methods, the known advantages the confirmatory method provides, their patient population, and physician preference. The strategy will differ depending on your institution and practice needs.
References
- Clinical and Laboratory Standards Institute. Urinalysis: Approved Guideline—3rd edition. 2009.
- Froom P, Barak M. Cessation of dipstick urinalysis reflex testing and physician ordering behavior. American Journal of Clinical Pathology. 2012;137(3):486-489.
- Brunzel N.A. Fundamentals of Urine and Body Fluid Analysis. 3rd ed. 2013, St. Louis, MO: Elsevier Saunders.
