External Quality Control for PT and aPTT in a Peer Group Using In-house

Lee, Woong Soo; Park, Ile Kyu

Abstract

BACKGROUND
Coagulation studies are affected by the reagents and coagulometers that are used in the tests and it is therefore essential to compare the results within a peer group that uses the same reagents and coagulometer for an external quality control program. Because the domestic quality control program encompasses many different groups using different reagents and coagulometers, no comparison has been made among peer groups. Therefore, the authors performed a quality control program using in-house lyophilized plasma in a selected peer group. METHODS: Prothrombin times (PT) and activated partial thromboplastin times (aPTT) were tested using in-house normal and oral anticoagulant lyophilized plasma; the tests were performed for 50 consecutive days in four hospitals that were using the same coagulometer. The same PT reagents were used in all four hospitals. The international sensitivity index (ISI) was 1.32 for three hospitals and 1.47 for one hospital. Three hospitals used the same aPTT reagent. RESULTS: After lyophilization, there was no change in the PT results, but aPTT results were greatly prolonged. At four hospitals, the average international normalized ratio (INR) of normal lyophilized plasma was 0.94, 0.94, 0.95, and 0.82, while the average INR of oral anticoagulant lyophilized plasma was 2.18, 2.28, 2.21, and 1.87. The mean normal PT (MNPT) of three hospitals with ISI of 1.32 were 12.4s, 11.2s, and 12.3s, while the MNPT of one hospital with ISI of 1.47 was 12.5s. Average aPTT of normal plasma were 32.1s, 45.9s, 44.7s, and 44.3s while that of the oral anticoagulant plasma were 42.6s, 61.3s, 57.8s, and 55.6s. CONCLUSIONS: Since there are a great deal of difference in the results of coagulation study among the hospitals using the same reagents and coagulometers, it is utmost necessary to enforce a national level coagulation study quality control program in order to adopt proper oral anticoagulation therapy.