* Whereas the HLH-2004 protocol uses ferritin >500 ng/mL, we generally view ferritin >2000 ng/mL as concerning for HLH, and ferritin >10 000 as highly suspicious in pediatric patients.^46,47 

† Elevations above age-adjusted, laboratory-specific normal levels (defined as >2 SD from the mean) appear more meaningful than the original designation of “>2400 U/mL,” because of variations between laboratories.