A simplified thromboplastin calibration procedure for standardization of anticoagulant control

In thromboplastin calibration, the possibility of replacing fresh individual plasmas by pooled fresh plasmas (used immediately after preparation or after storage at -25 degrees C) or by pooled lyophilized plasmas has been investigated. It was found that the thromboplastin sensitivity ratios (TSR's) assessed with pooled fresh plasmas show no divergence from those obtained with the original Biggs/Denson calibration procedure. With pooled lyophilized plasmas a small divergence can be found in particular with so-called PIVKA-insensitive rabbit-tissue thromboplastins. Since, in contrast to the original procedure, only a limited number of determinations with pooled fresh or lyophilized plasmas are needed to obtain an accurate TSR value, the modification substantially simplifies thromboplastin calibration. Moreover, the technique using lyophilized plasmas can be applied in laboratories where an insufficient number of patients are available or none at all. However, as long as pooled lyophilized plasmas display a more or less pronounced activation, it might be preferable to restrict calibration to qualified expert laboratories, i.e. national reference laboratories. The merits of pooled lyophilized plasma are those of good stability even under the condition of accelerated degradation. They might be just as useful as thromboplastins for use as (long-term) reference material in the standardization and quality control program of manufacturers of thromboplastins, and for laboratorians preparing their own thromboplastin for the anticoagulant control. Conditions for the preparation and use of lyophilized reference plasmas have been worked out and are presented.