In vitro methods for qualitative screening and/or quantitative determination of the functional activity of components of the Protein C anticoagulant pathway of blood coagulation are described. The methods entail measuring the conversion rate of a substrate by an enzyme, the activity of which is related to the Protein C anticoagulant activity, in a blood sample of a human comprising coagulation factors and said substrate, after at least partial activation of coagulation through the intrinsic, extrinsic or common pathway and triggering coagulation by adding calcium ions; and comparing said conversion rate with the conversion rate of a normal human blood sample determined in the same way. The methods include the addition of additional metal ions to the sample to enhance activity, sensitivity and resolution. Kits and reagents for use in the methods are also provided.