Serum paraoxonase/arylesterase 1 (PON1), L-lactate dehydrogenase B (LDHB), and sex hormone-binding globulin (SHBG) are consistently high in RA sera, while complement C1q subcomponent subunit B (C1QB) and insulin-like growth factor-binding protein complex acid-labile subunit (IGFALS) are low in both MG and RA sera. Here, SHBG is linked to rheumatoid arthritis.