Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. When a patient has a hematocrit level of ≥55 percent and a normal PT and APTT, do you still correct sodium citrate and ask for a redraw? Is it crucial to ask for a redraw when the emergency department orders a stat PT and APTT?

A.July 2022—CLSI document H21-A5 addresses the need to adjust citrate concentration for patients with high hematocrits since hematocrits above 55 percent lead to a relative excess of citrate in blue top tubes that may cause prolonged clotting times. I am not aware of guidance that addresses the need to redraw a sample for which citrate has been adjusted if the prothrombin time (PT) and activated partial thromboplastin time (APTT) are normal, which means laboratory directors can use their discretion in managing such situations.

Our laboratory would allow the normal results to be reported since the high hematocrit may lead to erroneous prolonged clotting times but would not be expected to cause erroneous normal clotting times.

The decision whether to redraw should take into consideration which tests are ordered since expected effects and potential clinical significance may be different for different assays. Therefore, the laboratory’s written procedure outlining the handling of polycythemic specimens should address the potential for erroneous results for calcium-dependent clotting tests, including routine (e.g. PT, PTT) and specialized (e.g. clottable protein C, protein S) coagulation testing.

Clinical and Laboratory Standards Institute. H21-A5: Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline, 5th ed.; 2008.

College of American Pathologists. HEM.36900 Elevated hematocrits—coagulation. In: Hematology and coagulation checklist. Sept. 22, 2021.

Marlar RA, Potts RM, Marlar AA. Effect on routine and special coagulation testing values of citrate anticoagulant adjustment in patients with high hematocrit values. Am J Clin Pathol. 2006;126(3):400–405.