• Extremely low platelet count with otherwise normal clotting factors
  • Mild to moderately low red blood cell count
  • Elevated levels of LDH
  • Abnormal kidney function (measured with a lab test called creatinine)
  • Presence of schistocytes in blood smear


TTP: usually occurs when platelets stick together and hence form blood clots. Platelets use a molecule in the plasma called von Willebrand Factor (vWF) to hold themselves together in the form of a clot. If the vWF molecules become too long, the platelets will form clots even when they’re not supposed to.  Usually the body keeps vWF cut to exactly the right length with an enzyme called ADAMTS13.  In some cases TTP develops due to a shortage of that enzyme caused by one of the following:

  • a genetic problem that keeps you from producing enough clipping enzyme (congenital TTP)
  • an overly active immune system that attacks and destroys your supply of clipping enzyme

In summary, your body becomes unable to keep vWF short enough to prevent abnormal clot and damage to the small blood vessels of your body.

HUS: most often occurs when your body is exposed to a toxin usually after a bacterial infection of the intestines, causing bloody diarrhea. This toxin makes its way into the blood stream and damages endothelial cells in the kidney.  This triggers platelets to clot and red blood cells to burst as described above.  For unknown reasons aHUS usually occurs in children rather than adults.

Unfortunately, there are many less typical patterns of TTP (secondary TTP) and HUS (aHUS) that occur in patients with another chronic medical condition, which may have acted as a trigger. Examples of conditions that can lead to this atypical TTP and aHUS include pregnancy, organ transplant, and diseases like HIV, lupus, and cancer.

aHUS Resource Links