CHI3L1 and cystic fibrosis: Notably, YKL-40 levels in CF sputa and CF sera showed a broad range of detection from levels similar to healthy control levels up to 30-fold higher levels in CF patients compared to healthy controls (Figure 1A right graph).YKL-40 serum levels correlated positively with YKL-40 sputum levels in both CF patients (r = 0.69, p<0.01) and, to a lesser extent, healthy control individuals (r = 0.42, p<0.05).