MRX Protein C is a chromogenic test for quantitative determination of protein C activity in citrated human plasma which can be used as an aid in diagnosis of protein C deficiency. Protein C deficiencies, hereditary and/or acquired, increase the risk for developing thromboembolic disease. There are two different types of protein C deficiency; type I refers to reduced biosynthesis whereas type II is characterised by a decrease in functional activity. MRX Protein C measures protein C activity, thus covering both types of protein C deficiencies. MRX Protein C consists of two components: Protein C Activator and Protein C Substrate. When a plasma sample is mixed with the Protein C Activator, all functional protein C is activated. The level of activated protein C in the plasma sample is quantified by adding a substrate that is specifically hydrolysed by activated protein C. The pNA released when the substrate is cleaved is proportional to the protein C level in the sample.