In Von willebrand disease there will be abnormal aPTT and normal PT. Activated Paial Thromboplastin Time (APTT) Test This test measures how long it takes for blood to clot. It measures the clotting ability of factors VIII (8), IX (9), XI (11), and XII (12). If any of these clotting factors is too low, it will take longer than normal for the blood to clot. The results of this test will show a longer clotting time among some people with VWD. However, the results of this test will be normal among people with mild VWD. Prothrombin Time (PT) Test This test also measures the time it takes for blood to clot. It measures primarily the clotting ability of factors I (1), II (2), V (5), VII (7), and X (10). If the level of any one of these factors is too low, it will take longer than normal for the blood to clot. The results of this test will be normal among most people with VWD. Reference: GHAI Essential pediatrics, 8th edition