Assessment of HUS. Because there are no specific acute markers that distinguish aHUS from the other TMAs, a screening and treatment strategy for HUS will depend on the clinical presentation and the presumed diagnosis. In the absence of an easily identifiable cause of the TMA, a broader range of laboratory tests will be required to formulate a likely diagnosis. The other laboratory tests to consider when assessing patients with TMA are: ADAMTS13, C3, C4, CFH serology, CFI serology, methylmalonic acid (urine and plasma), homocystine, HIV, ANA, lupus anticoagulant, antiphospholipid antibody, and direct antiglobulin. In addition, very young patients should be evaluated for streptococcal infection as a possible cause of their HUS. Genetic testing should be done early in suspected cases of aHUS; however, treatment should not be delayed pending results.