6 nmol/L) and the average FNPP citrate concentration (18.
Underestimation of PT ratios with plasma R82A and overestimation of PT ratios with FNPP were observed as compared with PT ratios calculated with the use of the MNPT as the denominator term.
Because significant between-laboratory differences emerged in our analysis when the PTs of FNPP or of plasma R82A were used as denominator terms, the possibility of differences in the selection of the normal plasma samples among the participating laboratories cannot be ruled out.
In conclusion, full commutability of PT ratios obtained with a large series of PT systems with the use of the PT of the lyophilized plasma R82A or of FNPP was not achieved in this collaborative study, nor can it be obtained with the use of reagent-specific correction factors because of the separate effects of endpoint detectors and plasma citrate concentration.
5) Nonstandard abbreviations: PT, prothrombin time; MN PT, mean normal prothrombin time; FNPP, fresh normal plasma pool; INR, International Normalized Ratio.
PT, s (SD) Normal plasma samples FNPP R82A Arithmetic mean 15.
The 30 individual normal plasmas were tested in duplicate; the 5 FNPPs and the R82A plasma were tested in triplicate on each day.
Within-day, between-day, and total variations in the PT of the individual normal plasma samples, corresponding FNPPs, and plasma R82A were calculated for each PT system .
PT values of the 30 apparently healthy individuals tested in each laboratory with the different PT systems were expressed as PT ratios with the use of either the MNPT, the grand mean (arithmetic) PT of the 5 separate FNPPs, or the grand mean (arithmetic) PT of plasma R82A as the denominator term.
As expected, total and between-day variations were significantly higher with the FNPPs than with plasma R82A (P = 0.