Protein Z in healthy human individuals and in patients with a bleeding tendency

Protein Z is a vitamin-K-dependent plasma glycoprotein; its physiological function is not clear. Low protein Z levels were found in patients with otherwise unexplained bleeding disorders. It was therefore suggested that low protein Z levels might be associated with a bleeding diathesis. In the present study we measured protein Z levels in plasma samples of 48 patients with a suspected bleeding disorder and in plasma samples of 200 healthy adult individuals. We found protein Z to have a wide normal range in healthy men and women. Significantly lower protein Z levels were observed in women compared to men, whereas no correlation was found with age or other vitamin-K-dependent coagulation proteins. None of the 48 patients with a bleeding disorder had a protein Z level below the normal range. However, protein Z was significantly lower in the group of male patients with a bleeding history as compared to healthy men. In conclusion, our data indicate that low-normal protein Z levels are not associated with a bleeding tendency. However, it remains to be determined whether a low protein Z level is a weak cofactor associated with an increased bleeding tendency and whether decreased or absent protein Z (conditions not detected in our patients) might constitute a haemorrhagic diathesis.