Figure 3.

Diagnostic algorithm for screening and diagnosis of the different forms of thrombotic microangiopathy. In patients presenting with low platelet count, increased lactate dehydrogenase (LDH), and hemolytic anemia, plasma ADAMTS-13 activity should be measured: if <10%, this leads to diagnosis of thrombotic thrombocytopenic purpura (TTP). Positive tests for Shiga-toxin–producing bacteria in stools are consistent with a diagnosis of Shiga-like toxin–producing Escherichia coli hemolytic uremic syndrome (STEC-HUS). Diagnosis of atypical HUS (aHUS) is done by exclusion in patients in whom these tests are negative and with no evidence of secondary conditions. When aHUS is suspected, full screening for complement disease–associated abnormalities (complement factor H [CFH], membrane cofactor protein [MCP], complement factor I [CFI], C3, complement factor B [CFB], and thrombomodulin [THBD] mutations; CFH/CFHR rearrangements; and anti-CFH autoantibodies) should be performed. Genetic screening is being performed at the diagnostic level in several centers in Europe (http://www.orpha.net/consor/cgi-bin/ClinicalLabs_Search_Simple.php?lng=EN) and the United States, while detection of genomic rearrangements and anti-CFH antibodies is done only in few specialized centers for research purposes.