George, is there research available now that states a HCT >55% will not interfere with PT or PTT results? We struggle with the CAP requirement. We use a mechanical based method for PT and PTT within our organization.
Hello, and thank you for your question. The current CLSI guideline, Adcock DM, Hoefner DM, Kottke-Marchant K, Marlar RA, Szamosi DI, Warunek DJ. Collection, transport, and processing of blood specimens for testing plasma-based coagulation assays and molecular hemostasis assays; approved guideline–fifth edition, 2007. CLSI document H21-A5, requires citrate concentration adjustments for all patients with hematocrits over 55%, based on an in vivo study measuring 28 patients with hematocrits over 55%; Marlar RA, Potts RM, Marlar AA. Effect on routine and special coagulation testing values of citrate anticoagulant adjustment in patients with high mematocrit values. Am J Clin Pathol. 2006;126:400–5. An in vitro study employing 40 normal samples treated with varying citrate concentrations, Austin M, Ferrell C, Reyes M. Do elevated hematocrits prolong the PT/aPTT? Clin Lab Sci. 2013;26:89–94 concludes that while a statistically significant difference exists between high and normal hematocrit-related PTs and PTTs, the difference does not affect clinical management. The Austin group found, paradoxically, that citrate addition associated with shortening of 27/40 PTs and 23/40 PTTs.
Institutions continue to follow H21-A5, and the citrate volume adjustment requirement is necessary whether the instrument is electro-mechanical or optical, further, point-of-care PT/INR instruments only validate their instruments to HCTs between 25% and 55%, so polycythemic patient specimens are reflexed to the plasma-based assay.
Sorry to report conflicting findings, but unless CLSI H21 is revised, you should continue to follow the guideline and the CAP requirement. By the way, there is no need to adjust citrate volume for low HCTs. Geo.