aHUS is a form of TMA caused by overactivation of the terminal complement pathway.

TMA is defined as thrombocytopenia plus microangiopathic haemolytic anaemia (MAHA) and one or more of the following condition: renal impairment, neurological symptoms, gastrointestinal symptoms, visual symptoms, pulmonary symptoms and/or cardiovascular symptoms.^1,2

To establish an accurate diagnosis of aHUS, a number of tests may be performed.^7-10

ADAMTS13 activity can help identify or exclude thrombotic thrombocytopenic purpura (TTP).^1-2,5-6 ADAMTS13 activity >5% - 10% excludes TTP and supports a high likelihood of aHUS, and ADAMTS13 activity <5–10% supports a diagnosis of TTP.^†1,2

^†Range cut-off is dependent on the assay.¹

Shiga toxin or enterohemorrhagic e.coli (EHEC) tests can help identify or exclude shiga toxin-producing e.coli haemolytic uraemic syndrome (STEC-HUS).^1-2,5-6 Shiga toxin/EHEC positivity indicates STEC-HUS.^1,2

While awaiting ADAMTS13 results, a patient’s PLASMIC score can help: a score of 0–5 should raise suspicion of aHUS and a score ≥6 supports a diagnosis of TTP.^‡11-13

^†Range cut-off is dependent on the assay.^1
‡The PLASMIC score is a validated clinical prediction tool for the diagnosis of TTP associated with severe ADAMTS13 deficiency.^12,13

ADAMTS13 activity is central, in exclusion of TTP, for the diagnosis of aHUS.^1,2

Genetic testing is not required for a diagnosis of aHUS. In some patients, there may be no identified genetic variant; 30–50% of aHUS patients do not have an identified disease-causing genetic driver.^2,14-17

If aHUS is suspected but the expertise and testing facilities are not available, then urgent consultation with an expert is recommended.^2,13