Relationship between total prothrombin, native prothrombin and the International Normalized Ratio (INR).
Plasma levels of total prothrombin and fully-carboxylated (native) prothrombin were compared with results of prothrombin time (PT) assays for patients undergoing oral anticoagulant therapy. Mean concentrations of total and native prothrombin in non-anticoagulated patients were 119 +/- 13 micrograms/ml and 118 +/- 22 micrograms/ml, respectively. In anticoagulated patients, INR values ranged as high as 9, and levels of total prothrombin and native prothrombin decreased with increasing INR to minimum values of 40 micrograms/ml and 5 micrograms/ml, respectively. Des-carboxy-prothrombin increased with INR, to a maximum of 60 micrograms/ml. The strongest correlation was observed between native prothrombin and the reciprocal of the INR (1/INR) (r = 0.89, slope = 122 micrograms/ml, n = 200). These results indicated that native prothrombin varied over a wider range and was more closely related to INR values than either total or des-carboxy-prothrombin. Levels of native prothrombin were decreased 2-fold from normal levels at INR = 2, indicating that the native prothrombin antigen assay may be a sensitive method for monitoring low-dose oral anticoagulant therapy. The inverse relationship between concentration of native prothrombin and INR may help in identification of appropriate therapeutic ranges for oral anticoagulant therapy.
Braun
P J
PJ
Organon Teknika Corporation, Durham, NC 27704.
Szewczyk
K M
KM
D000284:Administration, Oral; D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use; D001774:Blood Chemical Analysis / Q000379:methods; D006801:Humans; D011516:Prothrombin / Q000032:analysis* / Q000737:chemistry; D011517:Prothrombin Time; D012016:Reference Values
D000925:Anticoagulants; D011516:Prothrombin