Editing Platelet (section)

==Measurement and testing==

===Measurement===
Platelet concentration in the blood (i.e. platelet count), can be measured manually using a [[hemocytometer]], or by placing blood in an automated platelet analyzer using particle counting, such as a [[Coulter counter]] or optical methods.<ref name="Stiff">{{cite book |last=Stiff |first=Patrick J. |url=http://www.ncbi.nlm.nih.gov/books/NBK262/ |title=Clinical Methods: The History, Physical, and Laboratory Examinations |date=1990 |publisher=Butterworths |isbn=978-0-409-90077-4 |editor-last=Walker |editor-first=H. Kenneth |edition=3rd |location=Boston |pmid=21250105 |editor-last2=Hall |editor-first2=W. Dallas |editor-last3=Hurst |editor-first3=J. Willis}}</ref> Most common [[complete blood count|blood testing methods]] include platelet count in their measurements, usually reported as [[complete blood count#Reference ranges|PLT]].<ref name="NHLBI">{{cite web |publisher=National Heart, Lung, and Blood Institute (NHLBI) |title=Platelet Disorders: Thrombocytopenia |date=24 March 2022 |url=https://www.nhlbi.nih.gov/health/thrombocytopenia |access-date=2022-11-18}}</ref>

Platelet concentrations vary between individuals and over time, with the population average between 250,000 and 260,000 cells per mm<sup>3</sup> (equivalent to per microliter), but the typical laboratory accepted normal range is between 150,000 and 400,000 cells per mm<sup>3</sup> or 150–400 × 10<sup>9</sup> per liter.<ref name="NHLBI"/><ref name="Stiff"/>

[[File:First and second wave of platelet aggregation.png|thumb|On for example optical densitometry, a first and second wave of platelet aggregation is seen, in this case for an [[adenosine diphosphate|ADP]]-initiated aggregation. ]]

On a stained [[blood smear]], platelets appear as dark purple spots, about 20% of the diameter of red blood cells. The smear reveals size, shape, qualitative number, and [[clumping (biology)|clumping]]. A healthy adult typically has 10 to 20 times more red blood cells than platelets.

===Bleeding time===
[[Bleeding time]] was developed as a test of platelet function by Duke in 1910.<ref name="Lind-485">{{cite book |last1=Lind |first1=Stuart E. |last2=Kurkjian |first2=Carla D. |editor1-last=Michelson |editor1-first=Alan D. |title=Platelets |date=2011 |publisher=Elsevier |isbn=978-0-08-046586-9 |oclc=162572838 |page=485 |edition=2nd |chapter-url=https://books.google.com/books?id=GnIQGmiSylkC&pg=PA485 |chapter=The bleeding time}}</ref> Duke's test measured the time taken for bleeding to stop from a standardized wound in the ear lobe that was blotted every 30 seconds, considering less than 3 minutes as normal.<ref>{{cite journal |vauthors=Duke WW |title=The relation of blood platelets to hemorrhagic disease |journal=JAMA |date=1910 |volume=55 |issue=14 |pages=1185–92 |doi=10.1001/jama.1910.04330140029009 |url=https://zenodo.org/record/1447283}}</ref> Bleeding time has low sensitivity and specificity for mild to moderate platelet disorders and is no longer recommended for screening.<ref>Mehic D, Assinger A, Gebhart J. Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause. Hamostaseologie. 2024 Jul 1. doi: 10.1055/a-2330-9112. Epub ahead of print. PMID 38950624.</ref>

===Multiple electrode aggregometry===
{{Main|Multiple electrode aggregometry}}
In [[multiple electrode aggregometry]], anticoagulated whole blood is mixed with saline and a platelet agonist in a single-use cuvette with two pairs of electrodes. The increase in impedance between the electrodes as platelets aggregate onto them, is measured and visualized as a curve.<ref>{{cite book |first1=Marco |last1=Ranucci |first2=Paolo |last2=Simioni |title=Point-of-Care Tests for Severe Hemorrhage: A Manual for Diagnosis and Treatment |url=https://books.google.com/books?id=7klECwAAQBAJ&pg=PA40 |year=2016 |publisher=Springer |isbn=978-3-319-24795-3 |pages=40–42}}</ref><ref>{{cite book |first1=Carlo |last1=Marcucci |first2=Patrick |last2=Schoettker |title=Perioperative Hemostasis: Coagulation for Anesthesiologists |url=https://books.google.com/books?id=e7WNBAAAQBAJ&pg=PA54 |year= 2014 |publisher=Springer |isbn=978-3-642-55004-1 |pages=54–56}}</ref>

{{Anchor|LTA}}

===Light transmission aggregometry===
In light transmission aggregometry (LTA), [[platelet-rich plasma]] is placed between a light source and a [[photocell]]. Unaggregated plasma allows relatively little light to pass through. After adding an agonist, the platelets aggregate, increasing light transmission, which is detected by a photocell.<ref name="Cuker2014">{{cite journal |last1=Cuker |first1=Adam |title=Light Transmission Aggregometry |journal=The Hematologist |volume=11 |issue=2 |year=2014 |issn=1551-8779 |doi=10.1182/hem.V11.2.2555}}</ref>

===Whole blood impedance aggregometry===
Whole blood impedance aggregometry (WBA) measures the change in electrical impedance between two electrodes when platelet aggregation is induced by an agonist. Whole blood lumiaggregometry may increase the test sensitivity to impairment of platelet granule secretion.<ref>{{cite journal |vauthors=McGlasson DL, Fritsma GA |title=Whole blood platelet aggregometry and platelet function testing |journal=Semin Thromb Hemost |volume=35 |issue=2 |pages=168–180 |date=March 2009 |pmid=19408190 |doi=10.1055/s-0029-1220325 }}</ref>

===PFA-100===
The [[PFA-100]] (Platelet Function Assay — 100) is a system for analysing platelet function in which citrated whole blood is aspirated through a disposable cartridge containing an aperture within a membrane coated with either collagen and epinephrine or collagen and ADP. These agonists induce platelet adhesion, activation and aggregation, leading to rapid occlusion of the aperture and cessation of blood flow termed the closure time (CT). An elevated CT with EPI and collagen can indicate intrinsic defects such as [[von Willebrand disease]], [[uremia]], or circulating platelet inhibitors. A follow-up test involving collagen and ADP is used to indicate if the abnormal CT with collagen and EPI was caused by the effects of acetyl sulfosalicylic acid (aspirin) or medications containing inhibitors.<ref>{{cite web |url=http://www.pathology.vcu.edu/media/pathology/clinical/coag/PFA-100FAQ.pdf |title=Platelet Function Assay FAQ |website=Department of Pathology |publisher=Virginia Commonwealth University |access-date=2017-03-27}}</ref> The PFA-100 is highly sensitive to von Willebrand disease, but is only moderately sensitive to defects in platelet function.<ref>{{cite journal |vauthors=Favaloro EJ, Pasalic L, Lippi G |title=Towards 50 years of platelet function analyser (PFA) testing |journal=Clin Chem Lab Med |volume=61 |issue=5 |pages=851–860 |date=April 2023 |pmid=35859143 |doi=10.1515/cclm-2022-0666 }}</ref>