Diagnostic Tests

CLINICAL ASSOCIATIONS

Mitogen’s ADAMTS-13 Activity and Autoantibodies / Inhibitors assay is a dual autoimmune and enzyme activity diagnostic test that is useful in the diagnosis of hemolytic/uremic syndrome (HUS), atypical hemolytic uremic syndrome (aHUS), and thrombotic thrombocytopenia purpura (TTP). ADAMTS-13 is a liver enzyme (metalloproteinase / zinc protease) that acts to cleave and degrade von Willebrand factor (VWF) (a protein that promotes platelet adhesion to sites of vascular damage). ADAMTS-13 also acts as a carrier protein for blood-clotting factor VIII in blood circulation.

Decreased or absent ADAMTS-13 activity is a characteristic feature of atypical hemolytic/uremic syndrome (aHUS). On the other hand, if the sample provided was found to be within normal limits (e.g. no laboratory evidence of ADAMTS-13 deficiency) a diagnosis of aHUS is unlikely. A normal ADAMTS-13 activity level does not exclude a diagnosis of thrombotic thrombocytopenia purpura (TTP) and therefore, clinical correlation is recommended. If a patient’s sample is found to be ABOVE the normal range for ADAMTS-13 ANTIBODY/INHIBITOR this is consistent with the presence of an autoantibody directed against ADAMTS-13. Absent or abnormally low ADAMTS-13 ACTIVITY levels along with the presence of an ‘inhibitor’ is a clinical feature of atypical hemolytic uremic syndrome (aHUS). A patient with an inhibitor but normal or increased ADAMTS-13 activity may have an autoimmune condition such as TTP. Clinical correlation is recommended and in cases of uncertainty the test should be repeated if clinically indicated.

Reference: J. A. Kremer Hovinga, S. R. Heeb, M. Skowronska, and M. Schaller. Pathophysiology of thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. J.Thromb.Haemost. 16:618-629, 2018.