Plasma Transfusion is Ineffective for Correcting Minimally Elevated INR
Wednesday, June 18, 2008
Today, much plasma is ordered prophylactically to correct an elevated protime (PT) prior to an invasive procedure. Physicians performing invasive procedures want to avoid hemorrhagic complications and often regard a mild elevation of a coagulation test result as an indication to order plasma. The decision to prophylactically transfuse plasma is based on three unproven assumptions. (1) Mild prolongation of PT/INR (defined as an INR <1.7) predicts bleeding from an invasive procedure. (2)Pre-procedure transfusion of plasma will correct a prolonged PT/INR. (3) Prophylactic plasma transfusions result in fewer bleeding events.
The evidence clearly contradicts the first assumption. PT and APTT begin to rise above the upper limit of the normal range when coagulation factor levels fall below approximately 70% of normal. When the INR increases to 1.3 - 1.5, vitamin K dependent coagulation factors are still 50% of normal. Even at an INR between 1.8 and 2.0, they remain at 30% of normal, which is still at or above the minimal hemostatic level of 20 -30%. These results explain why a mildly elevated PT/INR is not usually associated with spontaneous hemorrhage and does not increase the risk of bleeding during routine invasive procedures. Studies during the last 20 years in patients undergoing liver biopsies, bronchoscopic biopsies, renal biopsies, central line vein cannulation, thoracentesis and angiography have repeatedly demonstrated that PT and activated plasma thromboplastin time (APTT) are not predictive of hemorrhage. However, it must be remembered that the risk of bleeding is greater if the platelet count is decreased, platelet function is abnormal, or the patient has experienced massive trauma or is undergoing extensive surgery.
Additional evidence clearly disputes assumptions 2 and 3. Prophylactic transfusion of plasma to correct a mildly elevated INR prior to an invasive procedure is often not effective. When the INR is <1.7, transfusion of plasma corrects INR an average of only 0.1 per unit transfused, largely because the INR of plasma itself ranges between 1.0 and 1.3. The difference in coagulation activity between donor plasma and patient plasma is so small that plasma transfusions produce minimal demonstrable effect on the patient’s INR. While a patient with an INR of 1.7 or less may bleed during an invasive procedure, the medical literature clearly demonstrates that the incidence of hemorrhage is not different from that of patients with a normal INR.
In summary, plasma transfusion has minimal effect on normalizing the INR in patients with mildly prolonged INRs for the following reasons. (1) Plasma produced from healthy blood donors can have an INR as high as 1.3. (2) Plasma transfusion to a patient with an INR of less than 1.7 has minimal effect. (3) Plasma transfusion to patients with an INR of less than 1.7 does not decrease the INR more than usual medical care without plasma transfusion.
In view of this information, the common practice of prescribing plasma to correct a mildly elevated INR prior to an invasive procedure needs to be reevaluated. It is not necessary or efficacious to correct an INR below 1.7 to achieve adequate hemostasis.
posted by Fred Plapp @ 7:03 PM,
