Q&A column, 8/16

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Editor: Frederick L. Kiechle, MD, PhD

Submit your pathology-related question for reply by appropriate medical consultants. CAP TODAY will make every effort to answer all relevant questions. However, those questions that are not of general interest may not receive a reply. For your question to be considered, you must include your name and address; this information will be omitted if your question is published in CAP TODAY.

Q. If you obtain a platelet count from a blood sample collected in a sodium citrate tube, the result is multiplied by 1.1 to correct for the volumetric difference in anticoagulant compared with EDTA. When you result the platelet count from the sodium citrate tube, is it a CAP requirement to attach a comment such as: “_#__ Results reported from blue top tube. The reference range and other method performance specifications have not been established or approved by FDA. Use results with caution.”

A. The anticoagulant of choice when testing on a hematology analyzer is EDTA (purple top). Unfortunately, EDTA can also cause in vitro platelet clumping in certain individuals. When this occurs the standard practice is to collect a specimen with sodium citrate (blue top) as the anticoagulant. The blue top specimen must be filled fully to maintain the appropriate blood-to-coagulant ratio. The platelet results are then multiplied by 1.1 to obtain the final result. It is not required to add a disclaimer since this is a mechanism to correct a problem with the specimen and the original anticoagulant.

The CAP checklist requirement follows in its entirety, including references.

There is an adequate system (such as microscopic correlation with the blood film) to prevent reporting of spurious thrombocytopenia when platelet clumps, giant platelets, or platelet satellitism are present.

NOTE: When platelet satellitosis (satellitism), significant numbers of giant platelets and/or platelet clumps are suspected/detected by cyto/histographic abnormalities or instrument rejection of a platelet result, the platelet concentration must be independently verified. Correlation with a well-prepared blood film must be made. If platelets are clumped after collection in an EDTA-anticoagulated tube that was well-mixed at the time of collection, this may represent in vitro EDTA-induced changes; platelets should be quantified from blood collected directly into a counting diluent, or by use of a different anticoagulant (e.g. liquid sodium citrate with subsequent adjustment for dilution) or by estimation from a non-anticoagulated blood film.

Evidence of Compliance:

• Written procedure defining the methods used to detect spurious thrombocytopenia or platelet abnormalities and to correct results AND
• Record showing actions taken to verify platelet concentration prior to reporting.

References