[Prekallikrein deficiency: apropos of 2 cases].

An isolated, considerably prolonged aPTT (117 and 112 sec respectively; normal range 26-36 sec) was discovered during the preoperative workup in 2 patients aged 48 and 66 years. Both had a negative personal and family history for bleeding. Levels of the intrinsic coagulation factors which potentially cause a bleeding risk (VIII, IX, XI) were normal, and an inhibitor of the aPTT could not be detected. Investigation of the contact phase revealed a severe functional deficiency (less than 1%) of prekallikrein (PK) which was diagnostic of the homozygous state. Complete correction of the aPTT after prolonged activation of the contact phase and after addition of 0.2 volume of normal plasma to the sample is suggestive of this diagnosis, which needs to be confirmed by determination of the functional PK. Though deficiency of PK does not carry a bleeding risk, it is important to identify such cases in order to avoid time-consuming investigations in a surgical emergency situation.