Knowing your anti-coagulants and anti-platelets

I’ve noticed as a student that lots of people get them confused. It’s simple because they both thin the blood right?

Unfortunately, it’s not appropriate to mix up the two terms. Precision is key guys!

Want a quick two min crash course? Read on!

Anti-platelets

Affect primary hemostasis as they target platelet aggregation. Platelet aggregation involves linking to other platelets through fibrinogen through receptors called glycoprotein 2b3a (GP2b3a). This linking forms a platelet plug.

Antiplatelet

Aspirin – inactivates cyclo-oxygenase 1 (COX-1) there by reducing Thromboxane A2 (TXA2) which promotes aggregation. Clopidogrel – inhibit ADP dependent aggregation. This reduces the ability for the GP2b3a receptor to be expressed. GP2b3a antagonists (Abciximab) – prevents fibrinogen to bind to the receptor.

Anti-coagulants

Act on the coagulation cascade. The coagulation cascade occurs in secondary hemostasis with the primary goal to convert fibrinogen into fibrin. This would stabilize the platelet plug as fibrin a lot more stable than fibrinogen.

Anti-Coagulant

Warfarin – prevents the synthesis of Vit K dependent coag factors (2,7,9,10, C and S). Heparin – activates anti-thrombin 3 (AT3) and has an effect on thrombin and Xa. Low Molecular Weight Heparin – activate AT3 but only has an effect on Xa. Xa inhibitors – inhibit Xa. Direct thrombin inhibitors inhibits thrombin.

From this, I hope you can see why it’s very wrong to call warfarin an anti-platelet. Similarly, aspirin is not an anti-coagulant.

Three weeks in rural Australia – my John Flynn Placement experience

THE MEDICAL EXPERIENCE

The experience and knowledge that I acquired during the John Flynn Placement Program (JFPP) has surpassed all my expectations. It has encapsulated the beauty, challenge and excitement of rural medicine. I have had the opportunity to work within the local teaching hospital, assist in the operating theatre, consult patients within clinics, observe provision of youth mental health services through Headspace clinics, as well as flying to remote mines, communities and cattle stations with the Royal Flying Doctor Service (RFDS).

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Tests and markers in hemolysis

Direct and Indirect Coombs test:

Their use is to detect antibodies that BIND to the surface of red blood cells (RBC).
Basic principle:
     Anti-Human Globulins (AHG) are mixed with the patient’s RBCs. If the RBC has the antibodies attached, the AHG will bind to those antibodies and bind RBCs together. This will lead to agglutination – a visible clumping of red blood cells.

Direct Coombs’ test:

Is used to detect antibodies already attached onto the red blood cell. This could be for cases such as immune mediated haemolytic anaemias.

Steps:

  1. Add AHG to washed red cell
    • Washed = removing the patient’s own plasma
  2. Wait and see if there is agglutination.

Indirect Coombs’ test:

This test is used to determine antibodies in patient’s serum that is unbound to their red blood cells. This is useful in cases such as crossmatching prior to transfusion, and also in pre-natal screening of pregnant women.

Steps:

  1. Serum from the patient is cultured with RBCs of a known antigenicity from another patient.
  2. This process allows binding of antibodies to RBCs in vitro
  3. AHG then added to RBC
  4. Wait and see if there is agglutination
          Still unclear? Watch a youtube video

Serum Haptoglobin:

An indication of serum haptoglobin is to determine if hemolysis is present.
Haptoglobin is a protein produced by the liver and is found in the blood. Haptoglobin binds to free hemoglobin released from red blood cells. The Haptoglobin-hemoglobin complex will then be removed by the reticulo-endothelial system.
Hemoglobin is released in large quantities into the blood during hemolysis. This will cause lots of serum haptoglobin to bind to hemoglobin and consequently be removed.
Thus, during hemolysis, it is reasonable to expect haptoglobin levels to decrease.

Lactate Dehydrogenase (LDH) levels

Is an enzyme found in almost all cells. There are many indications to test for LDH levels. During haemolytic anaemias, the lysis of red blood cells causes a release of LDH into the blood. Thus it is reasonable to expect LDH levels as a marker of hemolysis.

Another indication for observing LDH levels is when the patient experiences muscle trauma or injury as it can also indicate tissue damage.

References:

  1. Kumar P, Clark M. Kumar & Clark Clinical Medicine. 5th ed. London: Elsevier limited; 2002.
  2. Hoffbrand A, Moss P. Essential Haematology. 6th ed. Oxford: Wiley-Blackwell; 2011.