Thrombosis with Thrombocytopenia Syndrome (also termed Vaccine-induced Thrombotic Thrombocytopenia) · Incidence is extremely rare.JumptoMainContentAmericanSocietyofHematologyCOVID-19ResourcesThrombosiswithThrombocytopeniaSyndromeEducationPublicationsAgendaforNematologyResearchRecommendationsAboutUsPrecisionMedicineGenomeEditingandGeneTherapyImmunologicTreatmentResearchSupportandFundingMeetingsCareersThrombosiswithThrombocytopeniaSyndrome (alsotermedVaccine-inducedThromboticThrombocytopenia)(Version1.4;lastupdatedApril29,2021)InputfromJamesB.Bussel,MD;JeanM.Connors,MD;DouglasB.Cines,MD;CynthiaE.Dunbar,MD;LauraC.Michaelis,MD;LisaBaumannKreuziger,MD;AgnesY.Y.Lee,MD,MSc;andIngridPabinger-Fasching,MD.KeyTakeawaysThrombosiswithThrombocytopeniaSyndrome(TTS)Diagnosis(mustmeetallfourcriteria):COVIDvaccine(Johnson&Johnson/AstraZenecaonlytodate)4to30dayspreviouslyVenousorarterialthrombosis(oftencerebralorabdominal)Thrombocytopenia*PositivePF4"HIT"(heparin-inducedthrombocytopenia)ELISAIncidenceisextremelyrare.RiskofdeathandseriousoutcomeofCOVID-19,includingthrombosis,faroutweighriskofTTSpossiblyassociatedwithhighlyefficaciousvaccines.UrgentmedicalevaluationforTTS isindicatedifanyofthefollowingdevelop4to30daysaftervaccination:SevereheadacheVisualchangesAbdominalpainNauseaandvomitingBackpainShortnessofbreathLegpainorswellingPetechiae,easybruising,orbleedingIfTTSissuspected,performimmediateCBCwithplateletcountandimagingforthrombosisbasedonsymptoms.Ifthrombocytopeniaorthrombosisarepresent,recommendurgentconsultationfromhematologistwithexpertiseinhemostasis.AvoiduseofheparinuntilTTShasbeenruledoutoruntilanalternativeotherplausiblediagnosishasbeenmade.Initialwork-up(anormalplateletcountislessconcerningforTTS*):CBCwithplateletcountandperipheralsmearImagingforthrombosisbasedonsigns/symptomsPF4-ELISA(HITassay);drawbloodpriortoanytherapiesFibrinogenandD-dimersInitiatetherapywithintravenousimmuneimmunoglobinandnonheparinanticoagulationpendingPF4ELISAresultsif:Signs/symptomsofseriousthromb