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Objectives To define a fit-for-purpose clinical outcome assessment, and thresholds for entry and improvement, of haemolytic anaemia, for inclusion as part of a novel multi-domain outcome measure for SLE clinical trials, Treatment Response Measure for Systemic Lupus Erythematosus (TRM-SLE).Methods An international working group comprising 12 clinicians (including adult and paediatric rheumatologists and a haematologist) and 4 patients with lived experience of haematological lupus activity completed a multi-step consensus process. First, the domain was defined and the scope of haemolytic anaemia for the SLE clinical trial context was enumerated. Candidate response measures were then nominated via an online survey, discussed and shortlisted. Shortlisted measures were evaluated via a systematic literature review (SLR) guided by COSMIN methodology focussing on relevant measurement properties and clinical trial utility. Informed by the SLR, the working group used nominal group technique (NGT) to reach consensus on a response measure, as well as entry, minimum and complete response thresholds.Results The domain was defined with 100% consensus as ‘immune-mediated haemolytic anaemia attributed to active lupus that impacts the patient and is modifiable by therapy to reduce or control disease activity’, and domain scope was defined to include Coombs’ positive autoimmune haemolytic anaemia and rarer subtypes ( figure 1). Six laboratory measures to fit this scope were shortlisted for the SLR, which screened 1,519 articles, of which 10 were included, including studies in non-SLE patient populations with autoimmune haemolytic anaemia. Consensus via NGT was reached on haemoglobin (Hb) improvement to measure haemolytic anaemia treatment response. Thresholds were defined for entry (Hb <10g/dL with laboratory confirmation of haemolysis), minimum clinically meaningful response (Hb improvement >2g/dL or Hb normalised with ongoing haemolysis) and complete response (Hb normalised and no laboratory evidence of haemolysis). These improvement thresholds correspond with previously published consensus response criteria for primary autoimmune haemolytic anaemia.Abstract PO:05:140 Figure 1Conclusions Consensus was reached to use Hb, with clinically meaningful thresholds for entry and improvement, to classify haemolytic anaemia treatment response in a novel multi-domain outcome measure for SLE clinical trials. This will improve the study of haemolytic anaemia and its treatment in SLE, and ensure that meaningful improvement contributes to the classification of treatment response.