THE IMPLEMENTATION OF THE WHO INTERNATIONAL NORMALISED RATIO (INR) SYSTEM OF PROTHROMBIN TIME STANDARDISATION

The implementation of the INR system has been assessed in a group of laboratories from over fifty countries. These centres participate in the World Health Organisation International Quality Control Programme in Blood Coagulation. Prothrombin times are performed on various lyophilised human coumarinised plasmas using both the local thromboplastin reagent and British Comparative Thromboplastin (BCT) reference preparation. During 1985 and 1986 a programme of education has been undertaken whereby instructions in the derivation of INR values have been given. The calculation of INR has been shown by means of a worked example and a chart for the conversion of the prothrombin ratio with BCT to INR was included. Prior to this, prothrombin results were expressed as British Corrected Ratios (BCR) with a minority of centres using INR. In 1984 the CV varied between 23.7% - 36.8% for results with local reagents, but between 8.2% - 14.3% with BCT. This suggested that conversion into INR/ BCR was unsatisfactory. The table shows the impact of the continuing educational programme.The number of laboratories expressing results as INR has steadily increased and the CV is now approaching that obtained with BCT. The improvement in CV suggests that the general application of the INR system will help improve inter-laboratory standardisation of oral anticoagulant control and should be encouraged.

A Simplified Electronic Permeameter Suitable for Routine and Standards Use

The complexity and range of types of available permeameter make inter-laboratory standardisation and commercial grading difficult. A simplified and inexpensive electronic permeameter offers the prospect of a readily specified standard instrument which is easy to use and rapid in action. A solid-state integrator replaces the usual electromechanical fluxmeter.