3- INR and APTT

KYJ3 - INR and APTT .
Knowing your Jargon- What is the difference?

Patients on Warfarin are often monitored with regular blood tests called International Normalised Ratio or INR for short.

Heparinised patients will have a blood test called Activated Partial Thromboplastin Time (APTT).

To understand the two tests you first need to understand how both the anticoagulants work

Heparin and Warfarin work differently.
Heparin destroys thrombin indirectly by stimulating an enzyme AT3.
Warfarin inhibits the precursor to Thrombin.  A protein called Prothrombin.

So when measuring Prothrombin Time (PT) the INR looks at how long prothrombin takes to convert into Thrombin.
If prothrombin is inhibited by warfarin, the prothrombin time is delayed.

With APTT, this test looks at the time it takes for Thromboplastin (sticky gooyness of plasma) to form once the test sample has been activated.

Nerdy topic, but I know you were wondering!