PReS-FINAL-2187: Use of screening tests in patients presenting to paediatric rheumatology with suspected haemophagocytic lymphohistiocytosis/macrophage activation syndrome

Introduction Haemophagocytic lymphohistiocytosis (HLH) is a severe condition in which there is extreme uncontrolled inflammation, and may progress rapidly to multi-organ failure and death. HLH may be genetic (primary HLH), or secondary to infection or autoimmune/ autoinflammatory conditions; if the latter, it is also referred to as macrophage activation syndrome (MAS). Distinguishing between primary HLH and MAS is challenging but important since the former requires different therapeutic approaches including allogeneic haematopoietic stem cell transplantation (HSCT) for long-term survival. HLH screening tests are now being used in patients presenting with suspected MAS. In systemic Juvenile Idiopathic Arthritis (sJIA), some patients demonstrate temporary perforin expression abnormalities that resolve with disease control. The utility of other screening tests in a rheumatology context is unknown.