Routine preoperative coagulation tests: an outdated practice?

Routine coagulation tests have been used for many years in the preoperative setting in the belief that they identify patients who may have acquired or congenital bleeding disorders, and on the assumption that testing will predict perioperative bleeding allowing treatment to be given and prevent it. Coagulation ‘screens’ typically include the prothrombin time (PT) and the activated partial thromboplastin time (APTT). Both tests were originally developed to aid in the diagnosis of inherited bleeding disorders such as haemophilia and were not intended as screening tests. Activation of coagulation can be achieved through the intrinsic or the extrinsic pathway leading to activation of the common pathway and conversion of fibrinogen to fibrin leading to clot formation. Although the cascade model of coagulation is not physiological, it is useful as a means to understand the mechanism by which traditional coagulation tests detect coagulopathies. The APTT activates plasma typically with substances such as kaolin or silica which cause activation of the contact pathway and, subsequently, the intrinsic and common coagulation pathways. A deficiency in any of these pathways will therefore prolong the APTT. The PT is activated with supraphysiological concentrations of tissue factor and detects FVII deficiency and also deficiencies in the common pathway. Both tests can also be prolonged by the presence of a lupus anticoagulant, inhibitors such as anticoagulants, and acute conditions associated with an acquired bleeding state. Inherited coagulation defects are rare. The incidence of haemophilia A and B is estimated at 1:5000 2 and 1:30 000 male births, respectively. Severe, clinically relevant, deficiencies of FII, FV, FVII, FX, and fibrinogen are even rarer with an incidence varying between 1:300 000 and 1:2 000 000, although this may be higher in populations where consanguineous marriages are more common. FXI deficiency is common in Ashkenazi Jews with a prevalence of 8% but rare in a general population. The majority of patients with these bleeding disorders will be aware of their diagnosis through either a personal or family history of bleeding and will be registered at specialized haemophilia centres. Indiscriminate screening by routine coagulation testing will therefore only very rarely identify previously undetected individuals. In contrast, prolongation of the APTT is a common occurrence with the most common reasons being mild FXII deficiency and the presence of a lupus anticoagulant, neither of which is associated with a bleeding tendency. Moderate and severe FXII deficiency was found in 2.3% of otherwise healthy Austrian blood donors and in 10.3% of patients undergoing cardiac surgery. Lupus anticoagulant can be found in 1.2–3.8% of healthy individuals, but the incidence increases with age and chronic disease, and was found in up to 30% of patients with systemic lupus erythematosus. The ability of a lupus anticoagulant to prolong the APTT or PT depends on the combination of reagents and analysers used and may therefore vary between laboratories. Other causes of a prolonged APTT not associated with a bleeding tendency include high molecular weight kininogen deficiency and prekallikrein deficiency. Finally, a normal range is calculated by the mean +2 standard deviations of measurements in healthy, non-bleeding subjects and by definition 2.5% of measurements in normal individuals will show a prolonged clotting time. Therefore, if routine coagulation testing is done to identify previously undiagnosed bleeding disorders, it is much more likely to identify a prolonged routine coagulation test that is not associated with a bleeding tendency. In practice, this can lead to further unnecessary Volume 106, Number 1, January 2011