European Concerted Action on Anticoagulation. Evaluation of a method for International Sensitivity Index calibration of two point-of-care prothrombin time (PT) monitoring systems (CoaguChek Mini and TAS PT-NC) with fresh plasmas based on whole-blood equivalent PT.
BACKGROUND
The International Sensitivity Index (ISI) calibration of whole-blood prothrombin time (PT) monitors for point-of-care testing (POCT) described by Tripodi et al. (Thromb Haemost 1993;70:921-4) has been shown to be dependable but is too complex and demanding. The use of plasma would simplify calibration of whole-blood POCT PT monitors, but important differences may exist between the ISI for whole blood and plasma calibrations.


METHODS
In a 10-center calibration study of two POCT whole-blood monitoring systems (CoaguChek Mini and TAS PT-NC), we characterized the relationship between the log PT for whole blood and fresh plasma with use of single lots of test strips/cards. This relationship (linear) was used to correct the difference between the whole-blood and plasma ISI. The reliability of the correction with different lots of test strips/cards was assessed at three centers. The linear relationship was used to correct the difference in the whole-blood and plasma ISI with four other lots of TAS PT-NC cards and with two additional lots of CoaguChek Mini test strips.


RESULTS
The correction decreased the ISI difference from 13.3% to 0.9% for the TAS PT-NC and from 5.7% to 0.6% for the CoaguChek Mini. In assessments at three centers, which included different lots of test strips/cards, the mean ISI difference was markedly decreased with the TAS PT-NC but not with the CoaguChek Mini, for which the mean ISI difference increased slightly.


CONCLUSIONS
The proposed correction resolves the discrepancy between whole-blood and fresh plasma ISI calibrations with TAS PT-NC test cards. The CoaguChek Mini systems could be calibrated without this correction.
D000818:Animals; D002138:Calibration; D005060:Europe; D006801:Humans; D007391:International Cooperation; D019934:International Normalized Ratio / Q000295:instrumentation; D010949:Plasma; D019095:Point-of-Care Systems; D011517:Prothrombin Time; D011817:Rabbits; D011934:Reagent Strips; D012015:Reference Standards; D013925:Thromboplastin / Q000592:standards
D011934:Reagent Strips; D013925:Thromboplastin