Summary
The fourteen types of thromboplastin included in the ICTH/ICSH Collaborative Study on Prothrombin Time Standardization were investigated with respect to their sensitivity for factor VII, activation products, and PIVKAs. All of these thromboplastins displayed sufficient factor VII sensitivity, and all were sensitive to activation products. After correction for the overall sensitivity slope, rabbit plain thromboplastins were the most sensitive preparations and human as well as rabbit diluted the least sensitive; bovine brain thromboplastin lost its exceptional position. Sensitivity to activation products explains why factors II, VII, and X present in artificially prepared abnormal plasmas may be difficult to assess accurately. Also, all thromboplastins appear to be sensitive for both PIVKA VII and PIVKA X. PIVKA VII acts as a procoagulant which increases the amount of factor VII measured by the one-stage assay technique. PIVKA X inhibits and thus reduces the activity of factor X. The procoagulant activity of PIVKA VII is particulary pronounced for the two lung-brain rabbit thromboplastins (Lyoplastin and Simplastin), whereas the anticoagulant action of PIVKA X is strongest with bovine brain thromboplastin (Thrombotest). Considered as a group, rabbit thromboplastins appear to be less sensitive for PIVKA X and more sensitive for PIVKA VII.
As judged from thromboplastin calibration results, all three types of lyophilized reference plasmas are to some degree distinguishable from fresh patient plasmas. Primary calibration of a thromboplastin must therefore still be performed with freshly prepared normal as well as patient plasmas.
