The main findings of the study were as follows: (1) the development of a specific and technically robust assay targeting the CALC2 sequence DQAAGGLRQH measuring the C-terminal pro-peptide of type II collagen; (2) CALC2 was generated by the BMP-1 cleavage of type II collagen; (3) the CALC2 level was increased in HEX supernatant in response to treatment with IGF-1, and the presence of CALC2 was further confirmed using Western blot analysis; (4) CALC2 levels were significantly lower in the patients with RA and AS than in the healthy controls. The gene discussed is IGF1; the disease is rheumatoid arthritis.