Plasma vs serum
Serum is plasma with no clotting factors in it. Everything has already been coagulated out. It is not a good decision to try to use serum to test for clotting ability because everyone will have haemophilia
As we have removed the plasma from the body it will have a tendency to try to coagulate. We pause this by adding sodium citrate which binds all the Ca2+ I think
Prothrombin time & International Normalised Ratio
This is a test for measuring the coagulation ability of the extrinsic pathway.
How does it work?
To a tube of plasma we add Ca2+, phospholipid and tissue factor, and we wait to see how long it takes to clot.
Normally the reference interval is 9-13 seconds.
If it is longer it indicates deficiency of factors 7, 10, and 5.
INR (International normalised ratio)
The INR is another quick calculation we do to normalise differences between different Prothrombin Time test kits. Often the main difference we account for is the tissue factor used, if its human, rabbit, or recombinant.
We calculate this via: Reference interval is 0.8-1.2 Target range for patient on warfarin is 2-3
Activated partial thromboplastin time
This is for testing the coagulation ability of the intrinsic pathway
How does it work:
You add kaolin or silica to a vial of plasma along with phospholipid and Ca2+ and check how long it takes to coagulate.
Normal time is 22-34 second. Longer time indicates possible deficency in Factors 8, 9, 12, 11, 10, or 5
Fibrinogen
Fibrinogen can be measured with an activity assay that is converted to units of mass.
Reference interval is 1.8-4.0 g/L
Coagulation factor assays
We can directly measure the level of activity that each clotting factor has via adding patient plasma to a synthetic plasma with none of the factor of interest in it.
Activity is measured as a percentage of normal clotting activity and the patient result is compared to a standard curve.
D-dimers
We can measure D-Dimer concentration to assess if there is a clot being made or broken down the the body. Which is cool ig. seems like it has minor significance.