VALIDATION OF CURRENT PRACTICE AND A NEAR PATIENT TESTING METHOD FOR ORAL-ANTICOAGULANT CONTROL IN GENERAL-PRACTICE

When oral anticoagulant control is monitored in general practice, veno us blood samples are usually transported to a central laboratory for d etermination of international normalized ratio (INR). An alternative i s near patient testing by a commercial method. In a rural general prac tice 27 km from a central haematology laboratory, whole blood samples were drawn from patients receiving oral anticoagulants and analysed by three methods: after centrifugation, plasma separated and frozen in l iquid nitrogen, transported to the laboratory, thawed and immediately analysed (control); courier transport of citrated sample to the labora tory for analysis (routine); near patient testing of whole blood sampl e (NPT). Maximum temperature achieved and time to analysis for routine samples were recorded. 306 complete sets of data were obtained. Compa rison between the routine method and the control method revealed accep table agreement. On multiple regression analysis, maximum temperature achieved did not contribute to differences observed but time to analys is of over 5 hours did make a significant contribution. Comparison bet ween the NPT method and control method showed acceptable agreement, wi th persistent under-recording by the NPT method. The routine method fo r INR determination was validated as robust and reproducible with the proviso that needle-to-analysis time should be kept below 5 hours. The NPT method was valid under conditions of normal general practice. Str ict quality control of NPT methods is essential if performance is to b e comparable with that of established methods.