Study patients
A total of 54 adult cases with newly diagnosed sHLH at the First Affiliated Hospital of Nanjing Medical University from November 2015 to December 2020 was enrolled. All the diagnosis of sHLH was based on the 2004 HLH Diagnostic Criteria16. The NK cells cytotoxicity assay was not applicable due to the limitation of technology. Excluded criteria included (1) history of rickets; (2) history of parathyroid or metabolic diseases; (3) use of over-the-counter or prescribed vitamin complements; (4) history of severe liver and kidney dysfunction.