Prothrombin time standardization and temperature problems.

The reaction temperature is crucial for enzymatic reactions. Difficulties in controlling the temperature in the tilt test tube technique for the prothrombin time test are illustrated. An improved detailed description of the technique is suggested for standardization purposes. Mixing of the specimen with the reagent should be done in the water bath. The test tubes should be immersed deeply into the bath. Recording of the temperature in the reaction mixture is recommended. When using plastic test tubes the temperature problems may be greater than with glass test tubes. Some heat denaturation of coagulation enzymes may take place at 37 degrees C. Lowering the temperature of the reaction to 30 degrees C and perhaps photometric recording of the coagulation should be included in a suggested future optimized reference method.