On September 12, 2016, Michelle Fahs MT (ASCP) asked about how to prepare tubes with the proper volume of anticoagulant for people whose hematocrit exceeds 55%. Here is a question from Sandy Odegaard asking about the correction formula’s derivation:
Hi George, BD could not explain where the conversion factor for calculating the appropriate sodium citrate volume came from: X = (100 – PCV) vol / (595 – PCV), where PCV = packed cell volume or hematocrit, X = volume of citrate anticoagulant and vol = volume of whole blood added to the tube. Do you have some knowledge of this? I would be very grateful. Thank you.
From George, I once had an article from the 1970s that provided the derivation of this formula as stated in the CLSI H21 format: C = (1.85 X 10 –e3) (100 – HCT) V, where C = volume of citrate anticoagulant, HCT is hematocrit in percent, and V is the volume of whole blood added. The article made it clear how the constant, 1.85 X 10 –e3 (.00185) was developed. Regrettably, I’ve lost the article, and am not enough of a mathematician to derive the formula on my own. I’ve been in the habit, like many, of simply applying the CLSI H21 nomogram.
The article, Marlar RA, Potts RM, Marlar AA, Effect on routine and special coagulation testing valused of citrate anticoagulant adjustment in patients with high hematocrit values. Am J Clin Pathol 2006:128; 400–5 provides evidence for the need for citrate sdjustment. They compared 28 high hematocrit patient results produced from standard and citrate-adjusted whole blood specimens and found significant differences for PTT, PT, fibrinogen, factor VIII, and protein C activity. In this study the authors withdrew the computed citrate volume to discard using a tuberculin syringe, thus maintaining the tube’s vacuum.
Participants, please respond with the derivation of the constant in the formula. Thank you.