English

Abstract

BACKGROUND Prothrombin time (PT) is routinely used as a test of coagulation. Thromboplastin is the key ingredient in the reagent for this test. Prothrombin time international normalized ratio (INR) readings can vary according to the thromboplastin used in the reagent. The composition of thromboplastin reagents can influence the sensitivity of each batch of reagents. Various thromboplastin reagents having different international sensitivity index (ISI) values are available now. This study was intended to evaluate the effect of different thromboplastins on INR reading for mitral valve replaced patients under stable oral anticoagulant therapy. METHODS The study was conducted on the citrated plasma received from the mitral valve replaced patients having stable international ratio between 2 to 3 for three months. 62 samples were collected from the clinical pathology laboratory, Govt. Medical College, Trivandrum. Each sample was tested with different thromboplastin reagents having international sensitivity index 1.0, 1.1 and 1.6 by measurement of the prothrombin time and conversion into international normalized ratio. The INR obtained from the thromboplastin with international sensitivity index 1.0 was considered as the standard. INR results obtained from samples tested with thromboplastin reagents with ISI 1.1 and 1.6 were compared with the standard by using analysis of variance (ANOVA) and Dunnett’s post hoc tests. RESULTS Sixty-two samples were tested with the thromboplastin reagent having ISI – 1.0, the mean INR is 2.42, for ISI – 1.1 mean INR value is 2.53 and for ISI 1.6, the mean INR value is 3.19. While comparing the mean value of INR for different reagents using ANOVA, the F value was 14.86, which was significant. P value less than 0.01. In the Dunnett post hoc test, the P value of difference between ISI 1.0/1.6 was < 0.01. Between ISI 1.1/1.6 also the P value is < 0.01. Both of these were significant. The P value of difference between the reagents having ISI 1.0 and 1.1 is 0.838 which denotes no significant difference. CONCLUSIONS In conclusion, the thromboplastin reagent with ISI 1.0 or nearest to 1.0 is most desirable for accurate INR report. KEYWORDS Prothrombin Time, International Sensitivity Index, International Normalized Ratio