What adjustment is needed to the citrate amount when performing INRs in severe pulmonary hypertension associated with cyanotic heart disease

2018-03-10 08:55:16

In this article The Adult Patient with Eisenmenger Syndrome: A Medical Update after Dana Point Part III: Specific Management and Surgical Aspects it says

Frequently, physicians do not appreciate inaccurate measurements of coagulation parameters if blood is withdrawn into regular tubes with a standard amount of citrate anticoagulant. Plasma volume is decreased in Eisenmenger patients due to secondary erythrocytosis and elevated hematocrit. Thus, the amount of citrate anticoagulant is excessive for patients with cyanosis and secondary erythrocytosis. Accurate measurement of coagulation factors requires adjustment of the amount of liquid anticoagulants according to the hematocrit level when hematocrit is higher than 55%.

So, how does one calculate exactly how much to reduce the citrate in the tubes to get an accurate INR?