Special Coagulation Testing
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What is Heparin?
An acidic unfractionized mucopolysaccharide that inhibits blood coagulation potentiating the action of Antithrombin
How is heparin given to a patient?
Must be given by injection
Where is heparin inactivated in the body, how is it excreted, and what is its half life?
Inactivated by the liver and excreted in the urineHalf life of one hour
How does heparin work as an anticoagulant?
- Enhances complexes between Antithrombin and activated serine proteases:
- Thrombin IIa, IXa, Xa, and XIa
- These complexes inactivate these serine protease factors
List 5 points of Standard heparin.
- 1. Continuous intravenous infusion
- 2. Best for surgical patients or pregnancy
- 3. High molecular weight 30,000-40,000 units
- 4. Maintains a therapeutic anticoagulationMeasured by APTT
List 5 points about Low Molecular Weight heparin.
- 1. LMWH is given as a subcutaneous injection
- 2. Longer half life than HMWH
- 3. Usually given once a day as a prophylaxis
- 4. Given as outpatient therapy as treatment for DVT
- 5. Reduces the risk of heparin-induced thrombocytopenia
Why should a heparin IV be stopped immediately after a bleeding episode occurs?
Heparin has an anti-platelet function.
What should you do if bleeding occurs following a subcutaneous injection of heparin?
- Protamine sulfate is given to inactivate heparin.
- Give 1mg of protamine for every 100 units of heparin
What is a side effect of heparin administration that occurs within the first 24 hrs. Why?
- Heparin-Induced Thrombocytopenia
- * Mild lowering of platelets occurs in the first 24 hours of heparin administration
- *Usually due to platelet clumping
- *Heparin binds to platelet factor 4 following the generation of an IgG antibody against heparin
- *Antibody of the heparin-Platelet 4 complex leads to platelet activation, thrombocytopenia, and thrombosis
What is warfarin aka Coumarin or Coumadin?
- 1. oral anticoagulant
- 2. vit k antagonist so decreases activity of factors II, VII, IX, and X
- 3. VII levels fall considerably w/in 24 hrs
How long does it take warfarin to reach its full anticoagulant effect? Why?
Takes three days for full anticoagulant effect due to plasma half life of Prothrombin
Describe the administration of an oral anticoagulant.
- *10 mg on day one, 5 mg on day two, 5 mg on day three, followed by PT monitoring
- *Adjustments should be made according to the PT result.
- *Maintenance dose ranges from 3-9 mg per day.
- *Lower loading dose is recommended for elderly patients
What control tests strongly evaluate the therapeutic response to oral anticoagulation? What are the ranges for the tests?
- *INR and PT
- *Patients in recovery from DVT, pulmonary embolism or inherited thrombophilia should have a INR range from 2.0 to 3.0
- *Patients with mechanical heart valves should have a therapeutic range from 2.5 – 3.5
What is Antiphospholipid Syndrome (APS)?
- 1. Persistence of an antiphospholipid antibody
- 2. Usually directed against GP 1B and Prothrombin
- 3. Lupus anticoagulant – Detected in patients with SLE
- 4. Associated with venous and arterial thrombosis
- 5. Autoimmune disorder of connective tissue
When is APS usually seen, what is it associated with, and how is it treated?
- 1. Usually seen after a lymphoproliferative disorder, post-viral infections
- 2. Associated with arterial thrombosis (stroke and myocardial infractions), Placental infarctions, and abortions
- 3. Treat with oral anticoagulants and maintain an INR greater than 2.0
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