Features:
(1) Onset of purpura with reduced platelet count about 1 week after a blood product transfusion. Patients may also show petechiae and ecchymoses.
(2) The patient is negative for a platelet antigen present in the transfused blood product. The most common specificity is anti-HPA-1a (anti-Pl-A1); other antibodies are directed against antigens on GPIIb/GPIIIa.
(3) The patients usually have a history of (a) previous platelet transfusion or (b) pregnancy (if female) as a sensitizing event.
(4) The patient's own platelets as well as any platelets carrying the target antigen are affected. Transfused platelets negative for the target antigen have reduced in vivo survival.
(5) Patients usually recover in 2 weeks but some patients have a delayed (2-3 months) recovery.
Therapy:
(1) Avoid platelet transfusions if possible. If necessary platelets from a target antigen negative donor can be used.
(2) RBC transfusions should be avoided. If necessary, washed cells or products from target antigen-negative donors should be used.
(3) Intravenous immune globulin is the treatment of choice.
(4) Plasmapheresis may be helpful in severe cases unresponsive to immune globulin.
Differential diagnosis:
(1) thrombocytopenia from underlying disease
(2) bacterially contaminated blood product
(3) drug-induced thrombocytopenia
(4) severe hemolytic transfusion reaction
(5) autoimmune thrombocytopenia
