CHI3L1 and acquired polycythemia vera: Out of the 21 cytokines assessed, the levels of C5a (P = 0.02), YKL‐40 (P = 0.02), IL‐2R (P = 0.01), IL‐8 (P = 0.033), IL‐7 (P = 0.006) and IL‐1 beta (P = 0.038) in PV patients were significantly higher than those in healthy controls (Figure 4A).