How blood stops bleeding

Coagulation & Clotting

Clotting is a chain reaction of proteins. When you bleed, factors activate like dominos to turn liquid blood into a solid plug. Too long → bleeding risk. Too short → unwanted clots.

Prothrombin Time (PT)
How many seconds it takes your blood to clot through the 'extrinsic' pathway.
INR (International Normalised Ratio)
A standardised version of PT used worldwide — especially to monitor warfarin.
Activated Partial Thromboplastin Time (APTT)
Tests the 'intrinsic' clotting pathway — used to monitor heparin treatment.
Fibrinogen
The protein that forms the mesh of every blood clot.
D-Dimer
A breakdown product released when the body dissolves a clot — used to screen for DVT and pulmonary embolism.
Thrombin Time (TT)
Measures the final step of clotting — converting fibrinogen to fibrin.