Coagulation Testing and Monitoring

Question 1

What are natural inhibitors of the coagulation cascade? What do they inhibit?

Answer 1

Antithrombin - inactivates 2, 9, 10, 11, 12
Protein C and S inactivates 5. 8
tPA - activates plasmin

Question 2

Name some Direct Thrombin inhibitors

Name some FXa inhibitors

Name an indirect FXa inhibitor

Answer 2

Direct Thrombin inhibitors:

• Argatroban
• Bivalirudin
• Dabigatran (PO)

FXa inhibitors:

• Rivaroxaban
• Apixiban

Indirect FXa inhibitors:
- Fondaparinux

Question 3

What is PT and what does it measure by what mechanism?

Sample:

Method:

Normal Range:

Answer 3

PT is prothrombin time and focuses on the extrinsic and common pathways

Sample: Plasma

Method: CaCl + patient tissue factor (time to clot)

Normal Range: varies (usually 11-15 seconds)

Question 4

What is aPPT and what does it measure by what mechanism?

Sample:

Method:

Normal Range:

Answer 4

aPPT is activated partial thromboplastin time

Sample: plasma

Method: CaCl + thromboplastin + patient plasma

Normal Range: varies (22-39 seconds)

Question 5

How do you calculate INR?

Answer 5

(Patient PT/ Control PT) ^ ISI

ISI = international sensitivity index

Question 6

What are anti-FXa levels and what does it measure by what mechanism?

Sample:

Method:

Normal Range:

Answer 6

Anti-FXa levels measure FXa inhibitory activity of antithrombin

Sample: plasma

Method: Add LMWH or UFH to plasma –> fixed amount of FXa –> inhibitory action –> measure residual FXa
- Residual Fxa is inversely proportional to [heparin]

Normal Range: w/o heparin it is 0

Question 7

What is ACT and what does it measure by what mechanism?

Sample:

Method:

Normal Range:

Answer 7

ACT is activated whole blood clotting time. Used to measure the anticoagulant effect of UFH of patients going through cardiac bypass surgery

Sample: POCT

Method: Fresh whole blood + activator = intrinsic pathway

Normal Range: don’t worry about it

Question 8

What is Fibrin D-dimer assay and what does it measure by what mechanism?

Sample:

Method:

Normal Range:

Answer 8

Fibrin D-dimer measures breakdown of cross-linked fibrin which produces D-dimer

Sample: Plasma

Method: antibodies target neo-epitope created by formation of D-dimers

Normal Range: mostly <0.5

D-dimers can be high if DVT/PEs are present

Question 9

What is TEG and what does it measure by what mechanism?

Answer 9

TEG is thromboelastography. Measures platelet interaction with coagulation cascade
-Used for cardiac surgery and liver transplantation

Sample: Whole blood

Method: Pin spins with blood and measures clotting time