February 2009

Editor:
Fredrick L. Kiechle, MD, PhD

Q. Once in a while we encounter a patient whose blood is EDTA-sensitive. What actions would you recommend taking to obtain an accurate CBC on such a patient? Also, if a hematology profile reports “unable to perform platelet count due to clumps,” how can you trust that the WBC is correct? Couldn’t the analyzer be counting platelet “clumps” as WBCs?

A. In vitro platelet clumping due to ethylenediamine­tetraacetic acid, or EDTA, anticoagulated blood may result in a falsely low platelet count (that is, pseudothrombocytopenia) by automated hematology analyzers. Moreover, automated hematology analyzers may count the platelet clumps as WBCs, resulting in a falsely elevated WBC count. Most hematology analyzers will flag the platelet count in some manner to alert lab personnel to “platelet clumping.” Good practice would indicate holding (not resulting) the automated platelet and WBC count until slide review and estimates can be performed.

Laboratories should have a procedure for estimating the WBC and platelet counts (CAP TODAY. December 2001;74). If the estimate of the WBC by slide review and the automated WBC count are within acceptable agreement limits established by the laboratory, the automated WBC count may be resulted. To overcome platelet clumping, the specimen may be reanalyzed after vortexing for two minutes to break up platelet clumps. If platelet clumping persists, the blood may be re-collected using sodium citrate as the anticoagulant (blue top tube). As a last resort, blood may be introduced directly into a BD Unopette or similar device for a manual count.

M. Ali Ansari-Lari, MD, PhD
Hematopathologist
Pathology Consultants of
South Broward
Hollywood, Fla.

Peggy Fuller, MT(ASCP)
Chief Medical Technologist
Memorial Regional Hospital
Hollywood, Fla.

Q. What are fasting guidelines for young children who are being tested for cholesterol, trigly­cerides, and so forth? Should infants and toddlers fast for 12 hours before such tests?

A. The American Academy of Pediatrics’ Committee on Nutrition published in 2008 its most recent guideline, titled “Lipid screening and cardiovascular health in childhood,” in the journal Pediatrics.¹ According to these guidelines, the recommendations from the National Cholesterol Education Program published in 1992 are still valid.² The guidelines state that if one of the parents has been found to have high cholesterol levels, a total nonfasting cholesterol measurement is recommended. If the total cholesterol is found to be elevated, =200 mg/dL, then the patient should return in a fasting state (overnight 12 hours) for a lipoprotein analysis (total cholesterol, HDL-C, LDL-C, triglycerides). Those with intermediate total cholesterol levels (170–199 mg/dL) should have their cholesterol measured again, and if the average of the two measurements is =170 mg/dL, a lipoprotein analysis is recommended.

If a patient has positive history of cardiovascular disease, then a fasting lipoprotein analysis is recommended as the initial screening.

References

1. Daniels SR, Greer FR, Committee on Nutrition. Lipid screening and cardiovascular health in childhood. Pediatrics. 2008;122:198–208.
2. III. The individualized approach: detection/diagnosis/evaluation. Pediatrics. 1992;89:545–554.

Amar Akhtar Sethi, MD, PhD
Department of Laboratory Medicine
Clinical Center
National Institutes of Health
Bethesda, Md.

Q. One of our cardiac surg­eons requests screening for cold autoantibody because during cardiac surgery the patient is cooled to 28° and to as low as 16°C. This, of course, is done by using ice-cold infusion. The American Red Cross screens for cold antibody at room temperature, 18°C, then 4°C. The two other hospitals in town only do the routine antibody screen with the gel method at 37°C. What is the best practice?

A. The concern about cold­reacting antibodies in cardiothoracic surgery has been around for decades. Since hypothermia is often induced during heart surgeries, some cardiothoracic surgeons request antibody screens at room temperature and colder. This controversy is best answered by a section in Mollison’s Blood Transfusion in Clinical Medicine: “As most cold alloantibodies are IgM and complement binding, the issue of clinical significance in patients subjected to artificial hypothermia recurs frequently. Most transfusion services have long ago abandoned antibody screening at temperatures below 30°C, and virtually all hospitals crossmatch blood at a temperature of 37°C, even for patients undergoing procedures that involve deep hypothermia. Given the dearth of adverse events reported, it is likely that cold alloantibodies inactive at 37°C but active at some lower temperature such as 25°C or 30°C rarely, if ever, cause clinically significant red cell destruction when the patient is cooled. Although some shortening of red cell lifespan may result from the cold alloantibody, accurate assessment of red cell survival is confounded by changes in blood volume induced by haemorrhage and transfusion.”¹

There are many anecdotal reports of problems occurring with cold agglutinins and how they can be avoided.^2,3 There are no good clinical studies to date, so we must rely on case reports, none of which are strongly compelling. The best argument for not routinely screening for cold antibodies in heart surgery again comes from Mollison: “Perhaps the most reassuring data involve in vivo survival of M (M+N-) red cells in two patients with anti-M studied during hypothermia. The low-titre, IgM anti­bodies did not react at 30°C. 51Cr survival studies performed with 2 ml of labelled blood documented normal circulation of M (M+N-) cells at 37°C, and no accelerated loss of these cells at blood temperatures between 16° and 28°C. One patient received 187 ml of MN (M+N+) red cells when the blood temperature was 25°C without evidence of a clinical transfusion reaction and without development of a positive DAT.”

References

1. Klein HG, Anstee DJ, eds. Effect of hypothermia on cold alloantibodies. In: Mollison’s Blood Transfusion in Clinical Medicine. 11th ed. Malden, Mass.: Blackwell Publishing; 2005:416.
2. Atkinson VP, Soeding P, Horne G, et al. Cold agglutinins in cardiac surgery: management of myocardial protection and cardiopulmonary bypass. Ann Thorac Surg. 2008;85:310–311.
3. Agarwal SK, Ghosh PK, Gupta D. Cardiac surgery and cold-reactive proteins. Ann Thorac Surg. 1995;60:1143–1150.

Lowell L. Tilzer, MD, PhD
Department of Pathology
and Laboratory Medicine
University of Kansas Medical Center
Kansas City

Member, CAP Transfusion
Medicine Resource Committee