CHI3L1 and rheumatoid arthritis: YKL-40 has also been studied in ANCA-associated vasculitis (AAV) which demonstrated strong cytoplasmic staining of YKL-40 in inflammatory lesions and up to 2 times higher median serum concentrations of YKL-40 compared to systemic lupus erythematosus, RA, osteoarthritis and healthy controls, P < 0.001.