title: Occurrence, etiology, and clinical significance of extreme thrombocytosis: a study of 280 cases.
abstract: OBJECTIVE
  To determine the etiology and to evaluate the clinical consequences of an extremely elevated platelet count.
  
  
  METHODS
  A review of the medical records was performed on all patients encountered during a 5 1/2-year period who had at least one platelet count of 1,000 x 10(9)/L or greater.
  
  
  RESULTS
  Of the total of 280 patients with extreme thrombocytosis (EXT), 231 (82%) had reactive thrombocytosis (RT), 38 (14%) had a myeloproliferative disorder (MPD), and 11 (4%) had cases of uncertain etiology. RT was more common than MPD in all age groups except those in the eighth decade and older. Symptoms of bleeding and/or vaso-occlusive phenomena were noted in association with EXT in 21 (56%) of the MPD patients but in only 10 (4%) of the RT patients. Treatment to lower the platelet count and/or inhibit platelet function was employed in 36 MPD patients and 23 RT patients. Eight patients with MPD and 34 with RT are known to have died, but no patient in either group is known to have died of a thrombotic or bleeding event when the platelet count was greater than or equal to 1,000 x 10(9)/L.
  
  
  CONCLUSIONS
  Platelet counts greater than or equal to 1,000 x 10(9)/L should not be considered rare events in the general, acute-care hospital population, and usually represent a reactive phenomenon.
authors.affiliation: Department of Pathology, Wake Forest University, Bowman Gray School of Medicine, Winston-Salem, North Carolina 27157-1072.
authors.forename: D H
authors.initials: DH
authors.lastname: Buss
authors.forename: A W
authors.initials: AW
authors.lastname: Cashell
authors.forename: M L
authors.initials: ML
authors.lastname: O'Connor
authors.forename: F
authors.initials: F
authors.lastname: Richards
authors.forename: L D
authors.initials: LD
authors.lastname: Case
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D010976:Platelet Count; D012189:Retrospective Studies; D013922:Thrombocytosis / Q000097:blood / Q000150:complications / Q000453:epidemiology* / Q000209:etiology*