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Stability of hematology panels.

Q Our physicians sometimes collect hematology specimens in the evening or over the weekend when the laboratory is closed. How long can these specimens remain at room temperature or in the refrigerator before being analyzed? We've measured hematology profiles collected on the same day and then 24 hours later; there appear to be no significant changes in the hemoglobin or leukocyte, erythrocyte, or platelet counts. The MCVs do seem to increase slightly, however. According to the manufacturer's directions, routine hematology specimens should be analyzed between 30 minutes and four hours after collection. Have studies been done to determine how long a hematology profile can stand (e.g., 24, 48, or 72 hours) before being analyzed? Will results change significantly after a prolonged delay? For best results, should the specimens be stored at room temperature or refrigerated?

A These are excellent questions There is a body of information that has been collected in some labs that will provide guidance. in our lab, for instance, we have been investigating the role of retained patient specimens for QC purposes for many years. The theory is that if a hematology specimen is analyzed while the instrument is "in control," it becomes, in effect, a secondary standard or control and then can be used later to check instrument performance. If the instrument is still in control, the repeat test should give essentially the same results. Thus it provides an economical QC system.

This question then arises: How much variation in the repeat test is acceptable? Several studies have been published on this subject. You should review them carefully if you wish to implement such a system.[1,2]

The stability of these panels has become a more important consideration in the last few years with the need for accurate, precise absolute lymphocyte counts in the diagnosis and treatment of AIDS patients. As you know, the diagnosis of this syndrome is based, among other things, on the measurement of the CD4+ lymphocyte count. Additionally, antibiotic prophylaxis, antiviral therapy, monitoring of treatment, and the determination of prognosis are all based on the CD4+ count, which is directly linked to the absolute lymphocyte count.[3]

How long can hematology specimens be saved before yielding unacceptable results? We have studied this question in some detail, comparing the stability of absolute lymphocyte counts in HIV-positive patients with our retained patient specimen experience. Both room temperature and refrigerated storage stability were studied for up to 72 hours. After 20 hours of storage at room temperature, about 10% to 15% of specimens from HIV-positive patients showed unacceptable variation (>20%); up to 25% of refrigerated specimens showed unacceptable results. After three days, one-third to almost half of the specimens gave unacceptable results.[4]

We reviewed our experience with the retained patient specimen data that served as the control for this study. These specimens are collected in EDTA and refrigerated overnight. As you also point out, these specimens seem to be reasonably stable for up to 20 hours. The total leukocyte counts and neutrophil counts tend to decrease (up to 10%), however, and the MCVs tend to rise slightly. Platelet counts and hemoglobin levels were stable.

It is probably reasonable to conclude that hematology data on specimens collected up to 24 hours earlier can be valid. Many referral labs have drawn this conclusion. Specimens held over the weekend can be more problematic. If, for instance, these specimens were drawn from a population in which there was a significant incidence of disease, the data might be flawed, as we have shown in HIV-positive patients.

We also collected anecdotal data on several different hematology analyzers that showed that some instruments have more of a problem with specimen stability than others. Therefore the prudent thing to do is to begin to generate a valid database on the stability of random hematology specimens. Do the initial count, store the specimens at room or refrigerator temperature for the time intervals you wish to investigate, and then repeat the blood count. Three specimens a day would be a reasonable number. After a month or so, evaluate your results. Have your medical director review the data and then institute or modify your policy based on solid evidence.

References

[1.] Hackney JR. The use of retained patient specimens for haematology quality control. Clin Lab Haematol 1990; 12(Suppl. 1): 83-89. [2.] Cembrowski GS, Lunetzky ES, Patrick CC, et al. An optimized quality control procedure for hematology analyzers using retained patient specimens. Am J Clin Pathol 1988; 89:203-210. [3.] Koepke JA, Landav AL. Precision and accuracy of absolute lymphocyte counts. Clin Immunol Immunopathol. 1989; 52: 19-27. [4.] Koepke JA, Smith-Jones M. Lymphocyte counting in HIV-positive individuals. Sysmex J Int. In press.
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Title Annotation:Tips on Technology
Author:Koepke, John A.
Publication:Medical Laboratory Observer
Date:Sep 1, 1992
Words:779
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