Q&A column

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.

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Q. Our lab does not have reference ranges established for body fluid manual differentials. Is it acceptable to use ranges from a reference material and include a disclaimer citing the source of the ranges?

A.July 2021—It is acceptable to use ranges from reference material for body fluid manual differentials, including cell counts from peritoneal, pleural, pericardial, and synovial fluids. This is reflected in the CAP hematology and coagulation checklist requirement HEM.36820 Reference Intervals. This checklist requirement was revised in September 2019 to include the following statement: “Reference interval citations from the manufacturer’s insert or published literature citations may be used to determine the reference interval.”¹ This may be most relevant for laboratories with relatively low test volumes for which establishing institutional reference intervals is not feasible.

Note that some published intervals from body fluid reference material may be based on total white blood cells rather than total nucleated cells. There are a number of clinical and practical reasons why the TNC count is preferred over the WBC count, including the desire to identify malignant non-WBCs and simplify chamber (hemocytometer) counts for low cellularity specimens. A checklist item recently underwent revision to reflect this; it will be published this fall. Please refer to a CAP TODAY Q&A by Megan Nakashima, MD, for a discussion of how automated body fluid cell counts should be reported.²