To investigate the prevalence of bleeding in heterozygotes for prothrombin deficiencies. Homozygotes or compound heterozygotes with Factor II (FII) levels of less than 10% of normal are always severely symptomatic.
On the contrary little is known about the heterozygous population who have FII levels around 40–50% of normal.
Forty-four patients heterozygous for this defect, in comparison with age and sex matched 44 unaffected family members, have been followed during a mean observational period of 22.5 years (range 4–35 years). The study was carried out in Padua between the years 1971 and 2010.
The mean prothrombin activity was 0.49 IU/dl (range 0.38–0.62) and 0.91 IU/dl (range 0.81–1.10) in the heterozygotes and in the normal counterparts, respectively.
In total, 14 patients showed bleeding manifestations vs. only three among the controls. Bleeding was sometimes spontaneous but more frequently occurred after tooth extractions, surgery, or delivery.
Some heterozygous patients had also to be given replacement therapy to control the bleeding. No substitution therapy was ever needed for the normal counterparts.
The prothrombin activity levels in the patients who were symptomatic tended to be lower than in those who remained asymptomatic.
The difference in the frequency of bleeding and in the bleeding score between patients and unaffected family members was statistically significant (P = 0.007 and 0.0007).
Prothrombin levels of about 40–50% of normal may not represent well tolerated hemostatic levels in case of surgical procedures, tooth extraction, or delivery. These data may have general clinical significance even for patients who have acquired defects.