Table 1.

Methodologies, advantages, and drawbacks of functional assays.

Cell Environment	Test	Instrument	Principle of the Assay: Endpoint	Advantages	Drawbacks
Whole Blood	Heparin-Induced Multiple Aggregometry (HIMEA)	Multiplate® analyzer	measurement of impedance increase due to platelet aggregation and deposition onto the electrodes	- no need for platelet isolation (whole blood) - easy to perform and rapid assay (one hour) - very good sensitivity: potential alternative to SRA	- need for each laboratory to determine its own cut-off - need for collection of donors’ blood into tubes containing hirudin
Platelet-Rich Plasma	Platelet Aggregation Test (PAT)/Light Transmission Aggregometry (LTA)	aggregometer (light transmission)	measurement of increase in light transmission due to platelet aggregation	- easily available in many laboratories	- performance highly dependent on the donor′s platelet (role of plasma environment) - time-consuming - large volumes needed
	Flow Cytometry (FCM)	flow cytometer	measurement of increase in P-selectin or phosphatidylserine expression on an activated platelet (HIT Confirm® assay and HIT Alert®)	- commercialized marked- in vitro diagnostic assay - performed in 2–3 h	- lower sensitivity than the reference test (i.e., SRA) - performance highly dependent on the donor’s platelet (role of plasma environment)
Washed Platelets	Serotonin Release Assay (SRA)	scintillation counter (β-radioactivity)	measurement of 14C-serotonin release from dense granules upon platelet activation	- rid of the inhibitory effect of plasma on platelet activation - considered “gold standard”	- platelet washing steps - use of radioelements (costly, specific agreement and premises) - time-consuming method: delayed results
	Heparin-Induced Platelet Aggregation (HIPA)	96-well plate with visual reading	visible macro-aggregates	- rid of the inhibitory effect of plasma on platelet activation	- platelet washing steps - lack of data on the performance - subjectivity of visual reading