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Laboratory features

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The laboratory findings in thrombotic thrombocytopaenic purpura include:

  • microangiopathic haemolytic anaemia:
    • fragmented red blood cells - schistocytes, helmet cells, triangle forms - in peripheral blood smear
    • normocytic, normochromic
    • Hb usually < 10 gm/dl
    • marked reticulocytosis; occasionally, nucleated RBC's
    • haemolysis - increased serum indirect bilirubin, LDH, and serum haemoglobin; absent haptoglobin
    • negative Coomb's test
  • thrombocytopenia - platelets usually < 50 000 per cu. mm
  • WBC's - normal or increased; neutrophils often increased
  • ADAMTS13 activity
    • severe deficiency of plasma ADAMTS13 activity (<10 IU/dL) with or without detectable inhibitory autoantibodies against ADAMTS13 supports the diagnosis of TTP if a patient presents with thrombocytopenia and microangiopathic hemolytic anemia (i.e. schistocytes, elevated serum lactate dehydrogenase, decreased hemoglobin and haptoglobin) without other known etiologies that cause thrombotic microangiopathy (TMA
    • normal to moderately reduced plasma ADAMTS13 activity (>20 IU/dL) in a similar clinical context supports an alternative diagnosis such as atypical hemolytic uremic syndrome (aHUS) or other types of TMA
  • coagulation tests - PT, PTT, fibrinogen - normal cf. DIC
  • elevated fibrin
  • urinanalysis - frequently, RBC's and protein; increased creatinine; rarely, oliguria
  • bone marrow - normal or increased megakaryocytes
  • gingival or skin biopsy may show capillary and arteriolar hyaline microthrombi, endothelial proliferation and subendothelial hyalinosis


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