Twenty-two studies investigated the association between IL-6 serum concentration at hospital admission and delirium during hospitalization (8, 13, 14, 16–18, 20, 21, 23, 25, 31, 37, 39, 42, 47, 48, 51, 52, 54, 57, 58, 60). This evidence concerns the gene IL6 and delirium.