Protein S and C Levels in Patients Receiving Coumadin Therapy

 

ratio of protein C to Factor 7 =

= (per cent normal activity protein C) / (per cent normal activity Factor 7)

 

ratio of protein S to Factor 10 =

= (per cent normal activity protein S) / (per cent normal activity Factor 10)

 

Interpretation:

• a ratio of protein C-to-Factor 7 < 0.7 is consistent with protein C deficiency

• a ratio of protein S-to-Factor 10 < 0.7 is consistent with protein S deficiency

 

Limitations:

This method can be misleading, especially in borderline deficiencies. Patients should be on stable dosing of anticoagulant. It is better to stop coumadin therapy and to perform testing after sufficient time (at least 1 week) for reversal of coumadin effect.