Abnormalities of clotting screen
| Abnormality | Cause | |
| Isolated prolongation of PT | 1. Vitamin K deficiency (HDN, malabsorbtion) | |
| 2. Liver failure | ||
| 3. (Warfarin) | ||
| Isolated prolongation of APTT | 1. VWD | |
| 2. Coagulation factor deficiencies: | ||
| • Factors VIII, IX and XI—clinically significant | ||
| • Factor XII—not significant | ||
| 3. Lupus anticoagulant—DRVVT | ||
| 4. (Heparin) | ||
| Combined abnormalities | 1. Liver failure | |
| 2. Vitamin K deficiency | ||
| 3. (DIC) | ||
| 4. Rare—afibrinogenaemia or dysfibrinogenaemia | ||
( ) Suspect in certain circumstances as described in text.