Detection of hemophagocytosis using serum laboratory tests includes soluble interleukin 2 receptor alpha chain (sCD25) and soluble CD163 (sCD163), a high affinity scavenger receptor for hemoglobin-haptoglobin complexes (Figure 1), both of which may be elevated, thereby suggesting sCD25 and sCD163 to be more sensitive in detection of MAS. Here, CD163 is linked to macrophage activation syndrome.