Laboratory tests revealed a progressive pancytopenia, including a sudden drop in hemoglobin from 10 to 6.8 g/dL, hyperferritinemia (5,129 ng/mL), elevated soluble IL-2 receptor (1,179 U/mL), mild hypofibrinogenemia, and positivity for PVB19 IgM. Here, CD40LG is linked to isolated hyperferritinemia.