Quick values that have been and are measured with different thromboplastins are not comparable. This is due to the different origin and production of the thromboplastins. This results in different Quick values in one and the same patient, measured on different systems. As early as 1983, the WHO approved a thromboplastin as a standard against which every manufacturer must calibrate his reagent. The sensitivity index ISI (International Sensitivity Index) must be close to 1. Since that time, the WHO recommends the INR = International Normalized Ratio for the output of the thromboplastin time determination.