HLH diagnostic and induction surveillance strategy. A complete diagnostic evaluation, thorough search for underlying triggers (including infection or malignancy), and assessment of relevant immune studies are indicated in patients suspected to have HLH. In addition, ongoing reevaluation of inflammatory markers is essential to gauge the response to therapy. ● represents recommended studies; and ○, recommended studies with sufficient clinical suspicion. Arrows indicate recommendations for initial daily labs with decreasing frequency to one study per week as values normalize. Italicized studies are those that may facilitate diagnosis but are not directly part of current diagnostic criteria. CT or abdominal ultrasound may also facilitate diagnosis by documenting splenomegaly. sCD25 and sCD163 are useful markers of inflammation that may be more reliable measures of HLH disease activity than ferritin in some patients. CD107 mobilization may corroborate NK functional studies and quickly indicate a relevant degranulation defect. Careful monitoring of infection status is appropriate when persistent viral (or other infection) is found. Initial viral PCRs should assess EBV, CMV, adenovirus, and other relevant viruses. CSF studies are important to determine CNS involvement of HLH, although MRI may be substituted initially in coagulopathic patients. Pan-CT may be helpful in cases where there is concern for abscess or underlying malignancy. EKG/echocardiogram establish baseline organ function and screen for coronary artery vasculopathy in patients with overlapping symptoms of Kawasaki disease. We also recommend initiating HLA testing at the time of diagnosis to avoid delays in identifying donors for HCT.