| PT / INR | Extrinsic + common (VII). Prolonged by warfarin, factor VII, liver disease, vit K deficiency. Monitors warfarin. |
| APTT | Intrinsic + common (VIII, IX, XI, XII). Prolonged by heparin, haemophilia A/B, vWD, lupus anticoagulant. Monitors unfractionated heparin. |
| TT | Fibrinogen → fibrin. Prolonged by low/abnormal fibrinogen and heparin. |
| Mixing 50/50 | Corrects = factor deficiency · Fails to correct = inhibitor (antibody). |
| Vit K factors | II, VII, IX, X + protein C & S. |
| HELLP | Pregnant, on pre-eclampsia background → deranged LFTs + haemolysis + low platelets. |
| TTP | Pentad: MAHA, ↓platelets, fever, renal, neuro. Normal coag screen. ADAMTS13 deficiency → treat with plasma exchange. |
| HUS | MAHA + ↓platelets + acute kidney injury. Child, post E. coli O157 diarrhoea. |
| DIC | ↑PT + ↑APTT + ↓fibrinogen + ↑D-dimer. Sepsis, trauma, malignancy, obstetric. |
| Platelets <50 | spontaneous bleeding risk begins |
| Platelets <10 | prophylactic platelet transfusion (no bleeding) |
| Neutrophils <0.5 | severe infection risk |
| Neutrophils <0.1 >5 days | bacterial then fungal infection common |