Precision And Accuracy Of The International Normalized Ratio In Oral Anticoagulant Control

Abstract

Precision is defined as the agreement between replicate analyses of the same material. Within-laboratory precision of the prothrombin time (PT) and INR can be optimized by choosing an appropriate combination of thromboplastin and instrument. Accuracy (true value) of the International Sensitivity Index (ISI), required for the calculation of INR, depends on the choice of international reference preparation for the thromboplastin, and on the instrument used by the local laboratory. Interaction between thromboplastin and each patient’s individual coagulation factors influences the accuracy of the INR. The contributions of imprecision, inaccuracy, and interaction effects can be combined to calculate the total uncertainty of the INR using Tomenson’s equation. Confidence intervals for the INR were calculated in typical examples. The 95% confidence intervals of the INR around 3 are approximately as wide as currently recommended therapeutic target ranges.

Liver transplantation for erythropoietic protoporphyria liver disease

“…The laboratory data at the time of transplant included an average total bilirubin of 13.2 mg/dl (range, 4.2-35), creatinine of 0.9 mg/dl (range, 0.5-2.6), and INR (measured or estimated from available prothrombin times) of 1.6 (range, 1.0-2.1). 33 The estimated MELD score in the patients prior to transplant was 21 (range, [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Comparison of MELD, Child-Pugh, and Emory model for the prediction of survival in patients undergoing transjugular intrahepatic portosystemic shunting

“…As in the MELD model validation study (20), prothrombin index was converted to prothrombin time INR with a standard formula (26).…”

Discrepancies in International Normalized Ratio Results between Instruments: A Model to Split the Variation into Subcomponents

“…Differences in INR results between instruments are higher than would be expected from the imprecision of each of the instruments compared (7,20 ). The total uncertainty of INR results has been calculated (7 ) and 1 study has been performed to investigate differences in INR over time (21 ).…”

“…Nevertheless, harmonization of results from different laboratories remains challenging (3)(4)(5). Different types and sensitivities of thromboplastins (2 ) and interactions between thromboplastin and coagulation factors of individual patients may influence the accuracy of the instruments (4,6,7 ). Furthermore, 2 different methods, the Quick (8 ) and the Owren (9 ), are used in the operation of INR instruments, which may also cause discrepancies (3 ).…”