Laboratory features

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

Reference:

• NHS England (October 2022).Rituximab treatment for acute TTP: Clinical Commissioning Policy
• Saha M, McDaniel JK, Zheng XL. Thrombotic thrombocytopenic purpura: pathogenesis, diagnosis and potential novel therapeutics. J Thromb Haemost. 2017 Oct;15(10):1889-1900.