Summary
An alternative approach to INR estimation is for laboratories to calibrate their own
local system using calibrant plasmas supplied by manufacturers or reference laboratories.
The purpose of the present study was to investigate the within-laboratory variability
of a calibrant plasma procedure using various sets of lyophilized plasmas. INR had
been assigned to 13 calibrant plasmas in a previous multi-center study. Each of 10
other (“field”) laboratories measured PTs in the 13 calibrant plasmas and in 15 local
fresh coumarin plasmas, using three different thromboplastin reagents. Each fresh
coumarin PT was converted to INR using a calibration procedure with a set of 4 calibrants
(1 normal + 3 abnormals). The abnormals of each set were either coumarin or artificial
and were used with different assigned INR. When the INR had been assigned with a thromboplastin
brand identical to the thromboplastin in the field laboratory, the procedure was named
“reagent-specific” calibration. Otherwise the procedure was named “dissimilar” calibration.
Using “reagent-specific” calibration procedures, relatively homogeneous INR were obtained
for the fresh coumarin plasmas, whatever type of calibrant was used. In contrast,
discrepant INR were obtained when “dissimilar” cross-species calibration procedures
were used. The study was limited to 9 laboratories using the same type of coagulometer
and one using a different type.
Keywords
Prothrombin time - INR - thromboplastin - calibrant plasma
