Bleeding Tendency of Unknown Origin and Protein Z Levels

Abstract

Protein Z is a vitamin K-dependent plasma protein synthesized by the liver, with homology to the other vitamin K-dependent coagulation factors [1]. Hogg and Stenflo [2] demonstrated that protein Z promotes the interaction of thrombin with phospholipid surfaces in a Ca++ dependent manner. Human plasma protein Z levels, measured in adults as antigen by an ELISA method [3], showed wide variability with a mean value of 2.9±1 μg/ml. The behaviour of protein Z is similar to that of the other vitamin K-dependent factors involved in haemostasis, i.e., lower levels in pre-term and full-term infants [4], in patients on warfarin treatment [3], and in those with liver diseases [5]. Clinical expression of the other vitamin K-dependent factors in relation to their levels is fully understood, whereas, despite the fact that protein Z was described by Prowse and Esnouf twenty years ago [6], it is still not clear whether alterations of this compound have a clinical implication on the haemostatic balance. Nevertheless, Kemkes-Matthes and Matthes [7] reported that 21 out of 36 patients with bleeding tendency of unknown origin showed low levels of protein Z, suggesting that a protein Z assay must be included in order to diagnose clotting factor defects in bleeding patients.