Editing Platelet (section)

==Disorders==
Platelet disorders can occur because there are not enough platelets, too many platelets, or the platelets do not function properly.<ref name="Michelson" />{{rp|vii}}

Low platelet concentration is called [[thrombocytopenia]], and is due to either decreased production, increased destruction of platelets, or platelets being sequestered in another part of the body. Elevated platelet concentration is called [[thrombocytosis]], and is either [[congenital]], reactive (to [[cytokine]]s), or due to unregulated production: one of the [[myeloproliferative neoplasm]]s or certain other myeloid [[neoplasm]]s.

Normal platelets can respond to an abnormality on the vessel wall rather than to hemorrhage, resulting in inappropriate platelet adhesion/activation and [[thrombosis]]: the formation of a clot within an intact vessel. This type of thrombosis arises by mechanisms different from those of a normal clot: extending the fibrin of [[venous thrombosis]]; extending an unstable or ruptured arterial plaque, causing [[arterial thrombosis]]; and microcirculatory thrombosis. An arterial [[thrombus]] may partially obstruct blood flow, causing downstream [[ischemia]], or may completely obstruct it, causing downstream [[infarction|tissue death]].:<ref name="Michelson" />{{rp|vii}}

{{Comprehensive table of platelet aggregation disorders and agonists}}
===Thrombocytopenia===
* [[Immune thrombocytopenia]] (ITP) — formerly known as immune thrombocytopenic purpura and idiopathic thrombocytopenic purpura
* [[Splenomegaly]]
** [[Gaucher's disease]]
* Familial thrombocytopenia<ref>{{cite journal |last1=Warren |first1=JT |last2=Di Paola |first2=J |title=Genetics of inherited thrombocytopenias. |journal=Blood |date=2 June 2022 |volume=139 |issue=22 |pages=3264–77 |doi=10.1182/blood.2020009300 |pmid=35167650 |pmc=9164741}}</ref><ref>{{cite journal |last1=Pecci |first1=A |last2=Balduini |first2=CL |title=Inherited thrombocytopenias: an updated guide for clinicians. |journal=Blood Reviews |date=July 2021 |volume=48 |pages=100784 |doi=10.1016/j.blre.2020.100784 |pmid=33317862 |s2cid=229178137}}</ref>
* [[Chemotherapy]]
* [[Babesiosis]]
* [[Dengue fever]]
* [[Onyalai]]
* [[Thrombotic thrombocytopenic purpura]]
* [[HELLP syndrome]]
* [[Hemolytic–uremic syndrome]]
* [[Drug-induced thrombocytopenic purpura]] (five known drugs — most problematic is [[heparin-induced thrombocytopenia]] (HIT)
* Pregnancy-associated
* Neonatal alloimmune associated
* [[Aplastic anemia]]
* Transfusion-associated
* [[Pseudothrombocytopenia]]
* [[Vaccine-induced immune thrombotic thrombocytopenia]] (VITT)

===Altered platelet function===
* Congenital
** Disorders of adhesion
*** [[Bernard–Soulier syndrome]]
** Disorders of activation
*** Disorders of granule amount or release
*** [[Hermansky–Pudlak syndrome]]
*** [[Gray platelet syndrome]]
*** ADP receptor defect
*** Decreased cyclooxygenase activity
*** [[Platelet storage pool deficiency]]
** Disorders of aggregation
*** [[Glanzmann's thrombasthenia]]
*** [[Wiskott–Aldrich syndrome]]
** Disorders of coagulant activity
*** [[COAT platelet defect]]
*** [[Scott syndrome]]
* Acquired
** Disorders of adhesion
*** [[Paroxysmal nocturnal hemoglobinuria]]
*** [[Asthma]]<ref name="pmid17654302">{{cite journal |vauthors=Kornerup KN, Page CP |title=The role of platelets in the pathophysiology of asthma |journal=Platelets |volume=18 |issue=5 |pages=319–328 |date=August 2007 |pmid=17654302 |doi=10.1080/09537100701230436 |s2cid=7923694}}</ref>
*** [[Aspirin-exacerbated respiratory disease]] (AERD/Samter's triad)<ref name="pmid22262771">{{cite journal |vauthors=Laidlaw TM, Kidder MS, Bhattacharyya N, Xing W, Shen S, Milne GL, Castells MC, Chhay H, Boyce JA |title=Cysteinyl leukotriene overproduction in aspirin-exacerbated respiratory disease is driven by platelet-adherent leukocytes |journal=Blood |volume=119 |issue=16 |pages=3790–8 |date=April 2012 |pmid=22262771 |pmc=3335383 |doi=10.1182/blood-2011-10-384826}}</ref>
*** [[Cancer]]<ref>{{cite journal |vauthors=Erpenbeck L, Schön MP |title=Deadly allies: the fatal interplay between platelets and metastasizing cancer cells |journal=Blood |volume=115 |issue=17 |pages=3427–36 |date=April 2010 |pmid=20194899 |pmc=2867258 |doi=10.1182/blood-2009-10-247296}}</ref>
*** [[Malaria]]<ref>{{cite journal |vauthors=Pleass RJ |title=Platelet power: sticky problems for sticky parasites? |journal=Trends in Parasitology |volume=25 |issue=7 |pages=296–9 |date=July 2009 |pmid=19539528 |pmc=3116138 |doi=10.1016/j.pt.2009.04.002}}</ref>
*** Decreased cyclooxygenase activity

===Thrombocytosis and thrombocythemia===
* Reactive
** Chronic infection
** Chronic inflammation
** Malignancy
** Hyposplenism (post-splenectomy)
** Iron deficiency
** Acute blood loss
* [[Myeloproliferative neoplasm]]s — platelets are both elevated and activated
** [[Essential thrombocythemia]]
** [[Polycythemia vera]]
* Associated with other myeloid neoplasms
* Congenital