Increased time to coagulation in the prothrombin time test, which is a measure of the extrinsic pathway of coagulation. The results of the prothrombin time test are often expressed in terms of the International normalized ratio (INR), which is calculated as a ratio of the patient's prothrombin time (PT) to a control PT standardized for the potency of the thromboplastin reagent developed by the World Health Organization (WHO) using the formula: INR is equal to Patient PT divided by Control PT. The phenotype is Prolonged prothrombin time (Human Phenotype Ontology identifier HP_0008151). Also known as: Increased INR, Increased international normalised ratio, Increased international normalized ratio, Low factor II activity, Prolonged PT, Reduced factor II activity, Reduced prothrombin activity.