Contact factor pathway deficiencies do not cause surgical
bleeding but make
heparin monitoring by the activated partial thromboplastin time (APTT) and activated clotting time (ACT) unreliable.
Heparin monitoring during
cardiopulmonary bypass (CPB) surgery in these patients is particularly challenging. Here we describe
heparin monitoring during CPB using the chromogenic anti Xa assay in two patients with severe
factor XII deficiency (FXII < 0.01 U/mL) and one patient with severe
prekallikrein (
PK) deficiency (PK < 0.01 U/mL). Anti Xa levels of the three patients during CPB varied between 3.8 and 4.8 U/mL in keeping with a control group (mean anti Xa 4.5 U/mL and ACT > 480 s). There were no
bleeding or thrombotic complications. We also found that detection of severe
PK deficiency by the APTT in the PK deficient patient was dependent on the
reagent used and discuss the sensitivity of different APTT
reagents for contact factor deficiencies. We conclude that the sensitivity of APTT methods for contact pathway deficiencies is highly variable and although insensitivity is not a clinical problem in terms of
bleeding, it can be a cause of discrepancy between different APTT
reagents and the ACT. This can lead to
confusion about a possible haemorrhagic tendency and delays in surgery. If these patients need to undergo cardiac surgery requiring high dose
heparin treatment, monitoring by chromogenic anti Xa assay is a good alternative.