Is it necessary to use commercial WBC controls when using a Nageotte Counting Chamber for QC of leukoreduced blood products?

A colleague in Louisiana reports that her facility has been using a Nageotte counting chamber for several years to QC leukoreduced blood products. They perform approximately 60 white cell counts per month on platelet products and 12 per month on red cell products. They have been doing this QC without running daily commercial controls, because the filter manufacturer who helped set up their Nageotte procedure told them that they did not recommend the use of controls. However, recently one of their technologists questioned the practice of doing the manual white counts without running daily commercial controls. As a result of this concern, the laboratory began using a commercial "bi-level control" that is designed to monitor methods for quantitation of residual leukocytes in leukoreduced RBC and platelet products. The target values for Level I and Level II are 1 to 2 white cells per microLiter and 2 to 20 white cells per microLiter, respectively. They use separate controls for analyzing red blood cell and platelet products. The inquiring blood banker wonders if it is necessary to do these controls. They participate in the CAP survey for leukocyte-reduced product QC and they have an annual competency test for this procedure.

The following responses have been received.

ADDENDA April 16, 2003

1. A transfusion medicine physician in Boston (who works at the Massachusetts General Hospital Blood Transfusion Service, and who has a very "sunny" disposition) has shared the following opinion regarding the question, 'Are daily commercial controls for leukocyte counting required' He would argue "no". What follows is why he argues, NO. (verbatim)
   
   "There are a few parts to the answer:
   1. Commercial controls versus 'home-made' controls.
      There is no evidence that commercially prepared control leukocytes are any better than home-made control cells. The latter can be easily prepared by taking a specimen of normal blood and obtaining an accurate WBC count using a standard hematology analyzer. (Some test the sample several times and average the results.) The sample is then diluted using a VERY leukoreduced product. For example, a control specimen intended for testing leukocyte-reduced RBCs would dilute the sample using a diluent of 'very leukoreduced' rbcs (some labs might use twice filtered cells to achieve this diluent). For platelets, one can dilute a routine platelet concentrate with a diluent prepared from 'very leukoreduced' platelets. Commercial controls have the advantage of simplicity, and because they are generally preserved in fixative, have a longer shelf life.
   2. Should controls (whether commercial or home-made) be performed daily?
      The issue of whether controls should be run with each testing episode depends, in my personal view, on the importance of the testing. No one would consider running HIV-screening tests or ABO typing without appropriate controls because the consequences of reagent or test failure are substantial. On the other hand, many other tests in both general clinical medicine and laboratory medicine do NOT require controls at each episode of testing because the results are less critical. Leukocyte reduction, in my view, falls into this latter category because the process of leukoreduction confers no absolute benefit to the recipient. Therefore, my answer is No.
   3. Focus on people rather than on reagents. Leukocyte counting by Nageotte is much more dependent on human interpretation (like a WBC differential) than on machine calibration (like a pH meter). Thus, training/expertise is likely to be a more important area of variance than reagent performance. Therefore, laboratories concerned over results may wish to focus more on training to ensure proficiency."

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