A primary care evaluation of three near patient coagulometers

To compare the reliability and relative costs of three international normalised ratio (INR) near patient tests.

Protime (ITC Technidyne), Coaguchek (Boehringer Mannheim), and TAS (Diagnostic Testing).

All patients attending one inner city general practice anticoagulation clinic were asked to participate, with two samples provided by patients not taking warfarin. A 5 ml sample of venous whole blood was taken from each patient and a drop immediately added to the prepared Coaguchek test strip followed by the Protime cuvette. The remainder was added to a citrated bottle. A drop of citrated blood was then placed on the TAS test card and the remainder sent to the reference laboratory for analysis. Parallel INR estimation was performed on the different near patient tests at each weekly anticoagulation clinic from July to December 1997.

19 patients receiving long term warfarin treatment provided 62 INR results. INR results ranged from 0.8-8.2 overall and 1.0-5.7 based on the laboratory method. Taking the laboratory method as the gold standard, 12/62 results were < 2.0 and 2/62 were > 4.5. There were no statistical or clinically significant differences between results from the three systems, although all near patient tests showed slightly higher mean readings than the laboratory, and 19-24% of tests would have resulted in different management decisions based on the machine used in comparison with the laboratory INR value. The cost of the near patient test systems varied substantially.

All three near patient test systems are safe and efficient for producing acceptable and reproducible INR results within the therapeutic range in a primary care setting. All the systems were, however, subject to operator dependent variables at the time of blood letting. Adequate training in capillary blood sampling, specific use of the machines, and quality assurance procedures is therefore essential.