What is the platelet function analyzer 100 (PFA-100) and how is it used in the workup of platelet disorders?

Updated: Aug 05, 2017
  • Author: Perumal Thiagarajan, MD; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
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Answer

Answer

The platelet function analyzer 100 (PFA-100) is a bench-top automated instrument that assesses primary hemostasis under shear stress. The PFA-100 uses a disposable test cartridge that contains a membrane impregnated with collagen plus ADP (Col/ADP membrane) or epinephrine (Col/Epi membrane). A blood sample of 0.8 mL of citrated blood is placed in a cup and is aspirated through the aperture. The shear stress and the agonists in the membrane activate platelets, leading to platelet aggregation.

The end point, expressed as closure time, is when blood flow stops because of occlusion of the aperture by platelet aggregates.

The platelet aggregate formation depends on (1) vWf binding to collagen-coated nitrocellulose membranes, (2) platelet adhesion to vWf via platelet GP Ib platelet activation, and (3) platelet aggregation mediated by the interaction of GP IIb/IIIa with vWf and fibrinogen.

Normal closure times range from 77 to 133 seconds for the Col/ADP membrane and 98-185 seconds for the Col/Epi membrane. The PFA-100 has been tested in persons with bleeding disorders. The closure time using the Col/Epi cartridge is abnormal in patients with congenital platelet function defects, von Willebrand disease, or aspirin ingestion, whereas the closure time with the Col/ADP cartridge is abnormal mainly in patients with von Willebrand disease or congenital disorders.

Aspirin prolongs the closure time 94% of the time with the Col/Epi cartridge and only 27% of the time with the Col/ADP cartridge. Glanzmann thrombasthenia, Bernard-Soulier syndrome, and most mild von Willebrand diseases are associated with a prolonged closure time with both cartridges, whereas a storage pool defect and giant platelet thrombopathy have a prolonged closure time only with the Col/Epi cartridge.

The advantages of this instrument include simplicity and reproducibility. The PFA-100 has been reported to have a coefficient of variation of less than 10%. It may be useful for determining global platelet function and for assessing the efficacy of antiplatelet therapy.


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