Platelet Function Testing with the PFA-100

Inherited and acquired disorders of haemostasis are important areas of coagulation monitoring. The global coagulation tests Quick and PTT and individual coagulation factor analyses are only capable of detecting plasma-related coagulation disorders and unable to identify platelet function disorders (inherited or acquired through medications) and Von Willebrand Disease. 
Following the general discontinuation of the use of in-vivo bleeding time as a determinant of primary haemostasis due to problems concerning standardisation, reproducibility, susceptibility and complexity, the Platelet Function Analyser PFA-100 has become widely used as a sensitive method for monitoring platelet function disorders and primary haemostasis.

PFA-100

Methodology:
PFA-100 simulates platelet‚Äźdependent haemostasis in vitro. Anticoagulated blood flows via a capillary through a small aperture in a collagen membrane coated with two different activating substances (epinephrine or ADP). The adhesion and increasing number of platelets aggregating at these apertures subsequently seal them. The time it takes for the blood flow to stop is measured as the closure time (CT).

Reference Ranges:
The two measuring cells have different reference ranges:  
Closure time with collagen/epinephrine (CT Col/EPI) 84-160 sec
Closure time with collagen/ADP (CT Col/ADP) 68-121 sec
These values apply to anticoagulated whole blood with a citrate concentration of 3.8 %.

For test material with a citrate concentration of 3.2 %, the following values apply:
Closure time with collagen/epinephrine (CT Col/EPI) 82-150 sec
Closure time with collagen/ADP (CT Col/ADP) 62-100 sec

Indications for the use of PFA-100:
To verify or exclude:

  • Inherited or acquired platelet function disorders (approx.70 % of perioperative bleeding is caused by primary haemostasis disorders (Koscielny et al. 2007).
  • For checking the effectiveness of therapy with platelet aggregation inhibitors

Test result interpretation:

  • Prolonged membrane closure times can indicate Von Willebrand Disease (with the exception of Type 2N) or thrombocytopathy. Coagulation disorders are rarely caused by genetic defects such as M. Bernard-Soulier or M. Glanzmann, and are far more likely to be medication-induced or the result of a range of diseases such as, amongst others, uraemia, cirrhosis and autoimmune diseases that affect platelet function.
  • The combination of a prolonged CT Col/EPI and normal CT Col/ADP is relatively specific for an aspirin-induced platelet effect and suitable for preoperative monitoring of aspirin, medication contain aspirin and NSAID. A prolonged epinephrine closure time can be used to diagnose patients who do not respond well to aspirin (so-called non-responders), who do not or inadequately respond to standard doses of aspirin and other platelet aggregation inhibitors, as well as patients with poor compliance. These kind of patients are at great risk of developing other blood vessel occlusions following myocardial infarction or stroke. The ability to identify so-called non-responders can significantly contribute to optimising treatment for this patient group.

Sample material:
Anticoagulated whole blood in (3.8 %) buffered citrate
Anticoagulated whole blood in (3.2 %) buffered citrate
EDTA tubes for determining haematocrit levels and platelet count

(Required haematocrit > 0.35 and platelet count > 150 G/l. Lower haematocrit and platelet counts will make the test less reliable).

Pre-analytical information:

  • Non-traumatic blood specimen collection
  • Tubes must be filled to precise level
  • Specimen must be carefully mixed without producing foam
  • Avoid haemolysis
  • Specimens must be transported at room temperature (not refrigerated)
  • Test must be performed within max. 4 hours

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