Assess for underlying malignancy in consultation with Oncology:- Imaging including PET-CT to evaluate for lymphoma- Biopsy of any suspicious imaging findings- Bone marrow aspirate/biopsy if not performed already- Determine OHI index (sCD25/Ferritin) to aid in diagnosis and prognosticate- Determine % activated CD8+CD38+HLA-DR+ lymphocytes to distinguish HLH from sepsisConsideration in patients undergoing chemotherapy. Here, CD38 is linked to lymphoma.