[How to interpret and pursue a prolonged quick time or APTT]

The standard hemostasis workup [quick time (QT), and activated partial thrombin time (APTT)] is very commonly prescribed but its interpretation is often difficult for practitioners who are not specialized in hemostasis. Here, we review the principles of the diagnostic approach to these tests. Only a very basic knowledge of the coagulation cascade is necessary to identify which clotting factor tests to prescribe and to interpret the results. Deficiency in several clotting factors suggests liver dysfunction, disseminated intravascular coagulation (DIC) or vitamin K deficiency. If a single factor is deficient, we review the different causes of acquired deficiencies and briefly discuss the characteristics of the different congenital defects, which generally require specialized management. Lupus anticoagulant is a common and generally benign cause of prolonged APTT to be aware of, which is not related to a hemorrhagic risk. A good knowledge of the diagnostic approach to abnormal QT or APTT generally allows the resolution of the most common situations.