A COMPARISON OF ARTIFICIALLY-DEPLETED, LYOPHILIZED COUMARIN AND FRESHCOUMARIN PLASMAS IN THROMBOPLASTIN CALIBRATION

Artificially-depleted lyophilized plasmas and lyophilized coumarin pla smas were prepared and compared with fresh coumarin plasmas to assess their comparative reliability in local thromboplastin calibration usin g the manual prothrombin time (PT) technique. Their certified PT value s were inserted in turn on the vertical axis in place of the PT obtain ed with fresh coumarin plasmas. PT results were obtained at eight ECAA national laboratories ('test centres') and inserted on the horizontal axis. The resulting thromboplastin calibration slopes were compared w ith conventional fresh coumarin plasma calibration slopes at the same 'test centres'. When 60 artificially-depleted plasmas were substituted for 60 fresh plasmas, the mean calibration slopes with the human plai n International Reference Preparation (IRP) were 4.2% higher. For comp arison with 20 lyophilized coumarins, three sets of 20 artificially-de pleted plasmas were selected in sequential order from the 60. The lyop hilized coumarin plasmas gave a mean deviation of 9.6% from the fresh plasma calibration slopes compared with values of 2.0%, 6.1% and 11.7% for the three sets of 20 depleted plasmas. Although both types of lyo philized plasma calibration slopes give measurable differences from co nventional fresh plasmas, these may be regarded as acceptable in clini cal terms.