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CAP Home > CAP Reference Resources and Publications > CAP TODAY > CAP TODAY 2009 Archive > Q and A
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  Q and A

 

 

 

June 2009

Editor:
Fredrick L. Kiechle, MD, PhD

Question Q. We are trying to standardize urinalysis microscopic reporting and confirmatory testing. Are there references that address continuing to perform sulfosalicylic acid (SSA) testing for dipstick proteins or microscopy when urine glucose is greater than 1,000, or are these archaic ideas? We are finding it difficult to reach clinically relevant conclusions in the following areas: 1) Some of our sites still perform SSA testing for positive proteins when pH is greater than 8, and some do not. 2) Some sites perform a microscopic evaluation when the glucose is greater than 1,000, even if nothing else on the dipstick is abnormal. Most sites now reflex to the micro when the urine is not clear or there is positive blood, leukocyte esterase, or nitrite on the dipstick. 3) What should reporting intervals be for the microscopic? Are there guide-lines for re-porting elements in the microscopic? Is it clinically more useful to report as a number or to use few, moderate, many? 4) Should amorphous urates be reported as a crystal or as a separate entity? 5) Is it clinically significant to enumerate the presence of sperm, yeast, or Trichomonas, or can these be reported as “present” in the comments?

A. A complete urinalysis consists of three parts:

1) Examination of the physical properties of the urine (odor, color, clarity). Though these observations are important to patient care, they are not specifically addressed as “tests” by CLIA ’88 and may not always be a part of the information provided to the physician, particularly in point-of-care test-ing situations.

2) Chemical examination of the urine. Today, this testing is most often accomplished using multi-reagent dipstick technology and is classified as “waived.” Testing personnel are often nonlaboratorians and may not be familiar with the limitations of this technology, particularly the issues of false-positive and -negative results due to interfering substances in the urine.

3) Examination of the urinary sediment. This is classified as a moderately complex test, requires a trained and experienced laboratorian, and may require specialized equipment using flow technology or specialized microscopy.

These three parts of a urinalysis do not always occur in the laboratory, and delays in transport for microscopy may generate discordant results. The clinical laboratory may not be aware of test results obtained by others unless uniform, detailed, concise policies are developed and implemented along with documentation of competency by various testing personnel involved in all phases of testing.

When laboratory testing was centralized in the early 20th century, a complete urinalysis always included a microscopic examination of the sediment after concentrating the urine by a factor of 12:1 (centrifuging 12 mL of urine and discarding 11 mL of supernatant). This time-consuming procedure is now considered unnecessary if the urine is otherwise normal, and most reference texts now recommend limiting microscopy to abnormal urine specimens unless the physician specifically requests it. If this policy is adopted within the laboratory, it is important to recognize that abnormalities in color, clarity, and odor are just as important as a positive chemical test for blood, glucose, and so forth, and microscopy should be performed. Exceptions can be made for otherwise normal specimens with increased levels of bilirubin or urobilinogen, as neither of these substances reflects intrinsic renal disease. This decision should be made by the laboratory director and applied uniformly throughout the institution.

Quantitation of the formed elements in the urinary sediment is important primarily in establishing whether cells, casts, or crystals are present in abnormal numbers, because this information is clinically significant. Suggested reference values have been published, but appropriate institutional reference levels and reporting format should be established by the laboratory director in consultation with the medical staff. The report should be uniform throughout the institution and accompanied by reference ranges based on age and sex. Crystals should always be reported because the laboratory is often unaware of clinical circumstances that may be important, such as oxalate crystals in a patient with symptoms of renal colic. Even amorphous urates should be reported because their presence suggests that a specimen has undergone prolonged storage or otherwise been inappropriately handled and may need to be recollected. Most laboratories consider amorphous urates as crystals for reporting purposes. Whether to report exogenous entities such as sperm, Trichomonas, and yeast in a semiquantitative format or simply as “present” depends on the overall scope of laboratory activity. The labo-ratory director should make this decision. Again, reporting should be applied uniformly throughout the institution.

SSA testing to exclude proteinuria is not always done. The urinary dipstick test is sensitive only to albumin and will not react with globulins or abnormal free light chains (Bence Jones proteins). The only way to exclude proteinuria is to confirm a negative dipstick test for protein using SSA or a similar test. When using SSA, a precipitate may not form in highly alkaline urine because of insufficient acidification of the sample by the re-agent. This can be overcome by adjusting the pH of the urine before testing to a relatively normal value (pH 5-6). The SSA test will then be valid. Guidelines regarding patients who do not need to have negative dipstick tests for protein confirmed by SSA testing should be established by the laboratory director and applied uniformly across all testing sites.

Urines frequently contain interfering substances that can cause false-positive or -negative results with several of the reagents included in the dip-stick. Ascorbic acid, one of the most common interfering substances, can cause false-negative results for many tests. Self-administration of vitamin C during “cold and flu” season is common, and this preanalytic variable should be identified before testing. Seminal fluid in postcoital male urine specimens can cause a false-positive dipstick test for blood. Since specimens are often triaged by dipstick, testing personnel must be aware of situa-tions in which these results may need to be confirmed by another method in the laboratory, with this information incorporated into the final report.

Decentralized testing is increasingly common as screening laboratory tests move closer to the patient. This is true not only for urinalysis but also for testing in hematology, chemistry, microbiology, and immu-nology. These tests are all subject to preanalytic, analytic, and post-analytic variables, regardless of where testing is performed. To provide high-quality patient care, each laboratory must develop policies and procedures reflecting all of these phases of testing.

Bibliography

Ringsrud KM, Linne JJ. Urinalysis and Body Fluids: A ColorText and Atlas. St. Louis: Mosby-Yearbook Inc.; 1995

Ward PCJ. Medical Microscopy and Urinalysis. In: McClatchey KD, ed. Clinical Laboratory Medicine. 2nd ed. Philadelphia: Lippincott Williams and Wilkins; 2002: 499–552.

Mazouz B, Almagor M. False-positive microhematuria in dipsticks urinalysis caused by the presence of semen in urine. Clin Biochem. 2003;36:229–231.

David J. Blomberg, MD
Duluth, Minn.

Past member, CAP Hematology/Clinical Microscopy Resource Committee

Co-author, CAP Color Atlas of Urine Microscopy, set for publication in 2010

Question Q. Do I need to validate a blood transport cooler if I pack it according to the manufacturer’s instructions and the manufacturer has provided a qualification report and packing instructions with the products?

A. The use of transport coolers for blood products is wrought with controversy and logical inconsistencies. There is a table in the Code of Federal Regulations (21 CFR 600.15(a)) that lists the temperature requirements for “shipment” (transporting) of liquid red blood cells and liquid plasma (among other products). When specific requirements are listed, it is the facility’s responsibility to ensure that the conditions are met, either by direct monitoring (generally unsatisfactory for transport) or by validating that the conditions are met for a specified number of units for a specified period within a given environmental temperature range. The real controversy develops if an inspector or assessor determines that the transport container is actually being used for temporary storage rather than transport, because the temperature range becomes (illogically) more restrictive. Deviations that may affect the safety, purity, or potency of a blood product must be reported, even by transfusion services (21 CFR 606.171). Transport coolers must be validated like any other equipment used in the blood bank.

Information is available at www.fda.gov/ora/inspect_ref/igs/blood.html and respective CFRs at ecfr.gpoaccess.gov.

A. Bradley Eisenbrey, MD, PhD
Laboratory Director
Gift of Life Michigan
Ann Arbor

Question Q. Is there a consensus on whether you should wash patient red blood cells in saline once or twice when making a three to five percent cell suspension, in preparation for performing ABO/Rh typing on a patient?

A. The consensus among hospitals in southeastern Michigan is that they prepare red cell suspensions by dilution of a drop of whole blood with saline. If the forward and reverse typings are in consensus, the results are accepted. If, however, there is an ABO typing discrepancy, the patient’s red cells are washed once and retested.

Barbara O’Malley, MD
Associate Medical Director
of Transfusion Medicine
Harper University Hospital and
Children’s Hospital of Michigan
Detroit Medical Center


Dr. Kiechle is medical director of clinical pathology, Memorial Healthcare, Hollywood, Fla.
 
 
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