Destruction/consumption

• destruction (immunologic)
  • ITP
  • HIT
  • autoimmune/autoantibodies
  • alloantibodies: maternal, against donor plt
• MAHA
  • TTP
  • HUS
  • DIC
• mechanical shear: malig HTN, HELLP, valves

Abnormal distribution

• splenomegaly
• hypothermia: pooling in spleen
• dilution from transfusion
• pregnancy: plt > 70

Infection

• infection -> megakaryocyte apoptosis
• screen for HIV, HCV

Decreased megas

• aplastic anemia
  • Fanconi anemia
  • PNH
• (a)megakaryocytic anemia
• injury: chemorad, infection

Adequate mega number, but ineffective

• MDS
• platelet disease
  • MYH9
  • WAS
• ITP as dx of exclusion

Artifact: clumping, giant plt