Calcium Metabolism and Parathyroid Function in Rheumatoid Arthritis

In 40 patients with rheumatoid arthritis with various degrees of bone changes and 8 normal controls, serum calcium, inorganic phosphorus, chloride, alkaline phosphatase and parathyroid hormone were measured to assess the calcium metabolism and parathyroid function. Serum total calcium and serum calcium corrected by serum albumin were both significantly lower in patients with rheumatoid arthritis with advanced bone involvement than in controls, whereas serum inorganic phosphorus tended to be lower in patients with milder bone involvement. Serum Cl tended to be high in rheumatoid arthritis and serum Cl/P ratio was significantly higher than in the controls. Serum alkaline phosphatase was elevated in 5 of 14 cases of rheumatoid arthritis with advanced bone involvement. Serum parathyroid hormone was above the normal range in 12 of 21 cases of rheumatoid arthritis with no apparent bone changes, 2 of 3 cases with mild bone changes, and 9 of 14 cases with advanced bone changes. These findings would suggest parathyroid hyperfunction in rheumatoid arthritis without apparent correlation with the degree of bone involvement.