title: Platelet refractoriness to classical agonists in a child with essential thrombocythemia.
abstract: BACKGROUND
  Essential thrombocythemia is a rare disease during childhood. Platelet morphological abnormalities are frequent and defects in platelet function tests, mainly hypoaggregation, occur.
  
  
  METHODS
  An incidental diagnosis of essential thrombocythemia was established in a 9-year-old boy with a platelet count of 2050 x 10(9)/l. His platelets were studied for aggregation defects with four classical agonists employing optical aggregometry.
  
  
  RESULTS
  Aggregation ranged from 5% for adrenaline, 8% for collagen, 12% for ristocetin, to 25% with adenosine diphosphate, followed by complete disaggregation.
  
  
  CONCLUSIONS
  Platelet refractoriness to classical agonists, probably compounded by platelet GPIb deficiency, was documented. The differential diagnosis is discussed.
authors.affiliation: Autonomous University of Nuevo Leon, Monterrey, Mexico. carjaime@hotmail.com
authors.forename: Jose Carlos
authors.initials: JC
authors.lastname: Jaime-Perez
authors.forename: David
authors.initials: D
authors.lastname: Gomez-Almaguer
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000473:pathology; D002648:Child; D003094:Collagen / Q000494:pharmacology; D004351:Drug Resistance; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects; D010979:Platelet Function Tests; D012310:Ristocetin / Q000494:pharmacology; D013920:Thrombocythemia, Essential / Q000097:blood*
chemical_list: D012310:Ristocetin; D000244:Adenosine Diphosphate; D003094:Collagen; D004837:Epinephrine