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Tips from the clinical experts.

Answering your questions on which EDTA vacuum tubes to use, PSA reference values, and urine preservation for biogenic amine assays.

Which EDTA vacuum tubes should we use?

Q There have been articles in the literature that indicate we should consider changing our ethyl-enedamine tetraacetic acid (EDTA) hematology vacuum tubes from the tripotassium to dipotassium salt. Why have these recommendations been made? Should we switch?

A The International Council for Standards in Hematology (ICSH) has recommended the use of [K.sub.2]EDTA instead of [K.sub.3]EDTA.[1] This is based on the fact there is a small (1%) bias between hematocrits, depending upon the EDTA being used. In addition, European and Japanese laboratories use the [K.sub.2] salt, and if American laboratories would change, there would be a greater standardization of hematology methods.

You most likely will ask why the bother for a 1% change that hardly anyone would even notice, but it becomes apparent when manufacturers assign values to calibration materials for their hematology analyzers.

Further, the [K.sub.2]EDTA collection tubes have been used successfully in other countries; however, there was a tendency for microclot formation in these earlier EDTA tubes if they are not mixed adequately after collection. This was apparently caused by the dried powder used in the [Na.sub.2]EDTA tubes, whereas the [K.sub.3]EDTA tubes have an aqueous solution sprayed on the inner surface, which also causes about a 1% dilution of the blood specimen. Spraying [K.sub.2]EDTA solution into the new plastic tubes apparently has solved the problem of microclot formation as well as the 1% dilution.

Comparisons of the two potassium salts don't show any significant differences.[2-4] Only carefully performed reference methods can detect this dilution difference.[5]

So I would encourage you to switch to the [K.sub.2]EDTA plastic tubes for hematology testing. You will improve the accuracy of your tests.

-John A. Koepke

References

1. Recommendations of the ICSH for EDTA anticoagulation of blood for blood cell counting and sizing. Amer J Clin Pathol. 1993;100: 371.

2. Kane BK. Report on automated hematology testing using plastic tubes containing [K.sub.2] and [K.sub.3]EDTA compared to current [K.sub.3]EDTA tubes. San Jose, Calif.: Becton Dickinson; 1992.

3. Goosens W, Van Duppen V, Verwilghen RL, [K.sub.2]- or [K.sub.3]EDTA: The anticoagulant of choice in routine hematology? Clin Lab Haematol. 1991; 13:291.

4. Brunson D, Smith D, Bak A, et al. Comparing hematology anticoagulants: [K.sub.2]EDTA vs. [K.sub.3]EDTA. Lab Hematol. 1995;1:112-119

5. Koepke JA, et al. Standardization of EDTA anticoagulants for blood counting procedures. LabMedica. 1988-1989;5(6):12-1.

PSA reference values

Q What are the reference values for prostate-specific antigen (PSA)? Does the age of the patient play a role in the upper reference limit?

A The use of PSA in diagnosing prostate disease is very controversial. There is no doubt that prostate cancer is prevalent in men of advanced age. In fact, many have referred to prostate cancer as the male version of breast cancer. That's where the consensus seems to end. First, should all men be screened with regular PSA testing? Second, if the PSA value is elevated, what kind of therapy, if any, should be recommended? The reason there is so much uncertainty and debate is that most therapies have common side effects of impotence and incontinence. Furthermore, a more conservative approach of watching and monitoring the progression of the disease coupled with endocrine therapy and/or complementary therapy (e.g., nutritional therapy of a low fat diet and vitamins, exercise and meditation) in some hands have as good an outcome as the more conventional therapies. Finally, many individuals diagnosed with prostate cancer will die of some other disease because they contracted the cancer late in life and they will succumb to that other disease.

Theoretically there are three separate reference populations to consider for PSA values: men with prostate cancer, men without prostate disease, and men with benign prostate hypertrophy. The majority of older men suffer from minimal to moderate prostate hypertrophy. Thus, reference values have been determined on men without clinically evident prostate cancer. Anderson and coworkers[1] reviewed PSA measurements in 1,716 men without prostate cancer. They calculated the 95th percentile in each of a number of age groups:

* 40 to 49 years 1.5 ng/mL

* 50 to 59 years 2.5 ng/mL

* 60 to 69 years 4.5 ng/mL

* 70 to 70 years 7.5 ng/mL

The upper reference limits are not the same as the decision levels for PSA. One must take into account the reference values for patients with prostate cancer as well as the prevalence of cancer of the prostate in the population examined. Additionally, one also must consider the benefits and costs of the therapeutic measures and the expected mortality and morbidity of the disease.

- Bernard E. Statland

Reference

1. Anderson JR, Strickland D, Corbin D, et al. Age-specific reference ranges for serum prostate-specific antigen. Urology. 1995; 46:54-57

Urine preservation for biogenic amine assays

Q Concentrated HCl added as a preservative to 24-hour urine-collection containers for catecholamines, vanillymandelic acid (VMA), and metanephrines is a potential health hazard. Is there an alternative?

A This question was referred to Dennis Freer, PhD, co-technical director, Great Smokies Diagnostic Laboratory, Asheville, N.C. His answer follows:

Frequently, clinicians order multiple tests, including catecholamines and metabolites, on a single 24-hour urine collection. Since many other tests require boric acid as a preservative, we investigated whether boric acid would be an acceptable preservative for catecholamines and their metabolites. Also, we needed to be certain boric acid didn't interfere with our methods.

We did a prospective study in which an unpreserved urine sample was spiked with standards for catecholamines (epinephrine, norepinephrine, and dopamine) and with standards for metanephrine, nor-metanephrine, and VMA. Aliquots were prepared three different ways: 1) without preservative 2) with HCl added (pH 1-2), and 3) with boric acid at a concentration consistent with 15 g/24 hour collection.

All aliquots were then extracted and assayed by high-performance liquid chromatography with electrochemical detection. Repeat extraction and analysis also was performed after 48 hours of refrigerated storage.

Results indicated no significant difference between results for aliquots extracted on the date of preparation. For aliquots stored for 48 hours, there was an 18% loss of epinephrine in the unpreserved sample when compared with the preserved aliquots.

For the other catecholamines, metanephrines, and VMA, there was no significant difference between results for aliquots with no preservative, boric acid, or HCl. Subsequent studies using controls made up with and without preservatives (0.1 N HCl or boric acid) gave similar results.

Based on these data, boric acid was chosen as the preferred preservative since it does not have the safety hazard factor associated with 6N HCl and because it is a preservative required for many other tests that may be ordered in conjunction with catecholamines. We have done similar studies to confirm potassium bisulfate tablets also are an acceptable alternate preservative.

- Denis Freer

Edited by Bernard E. Statland, M.D., Ph.D., Statland Laboratory Consulting, Nashville, Tenn.

Panelists (name following each answer indicates respondent panelist):

Daniel M. Baer, M.D., Chief of Pathology, Veterans Affairs Medical Center, and professor of pathology, Oregon Health Sciences University, Portland, Ore. Kathleen G. Beavis, M.D., assistant director, microbiology laboratory, Thomas Jefferson University Hospital, Philadelphia, Pa. John A. Koepke, M.D., professor emeritus of pathology, Duke University Medical Center, Durham, N.C. Byron A. Myhre, M.D., Ph.D., professor of pathology and chief of clinical pathology, UCLA School of Medicine, Harbor General Hospital Campus, Torrance, Calif. Robert M. Nakamura, M.D., senior consultant and chairman emeritus, department of pathology, Scripps Clinic and Research Foundation, La Jolla, Calif.
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Article Details
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Title Annotation:clinical laboratories
Author:Koepke, John A.; Statland, Bernard E.; Freer, Dennis
Publication:Medical Laboratory Observer
Date:Dec 1, 1996
Words:1310
Previous Article:Familiar issues await lab industry in '97.
Next Article:Management Q & A.
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