While the diagnosis of HLH (through the HScore or the HLH-2004 criteria) can be made without biomarkers such as NK cell activity, s-IL-2r and soluble CD163, various studies (Table 1) have demonstrated the utility of decreased NK cell activity, increased s-IL-2r levels and increased soluble CD163 levels in primary and secondary HLH. This evidence concerns the gene IL2RA and hemophagocytic syndrome.