• Joost Jair van Veen, Stuart Laidlaw, Justin Swanevelder, Nicholas Harvey, Chris Watson, Steve Kitchen, and Mike Makris.
• Haemostasis and Thrombosis unit, Department of Haematology, University Hospitals Leicester NHS Trust, Leicester, UK. joost.vanveen@ukgateway.net
• Eur. J. Haematol. 2009 Mar 1;82(3):208-12.

AbstractContact 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.

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