Determinants of serum 1,25(OH)2D levels in renal disease

Serum 1,25(OH)2D and factors related to its production were studied in 39 patients with various degrees of renal insufficiency. Serum 1,25(OH)2D levels correlated positively with 1/serum creatinine values (r = 0.54, P less than 0.001) and negatively with serum phosphorus (r = -0.39, P less than 0.02) and age (r = -0.33, P less than 0.05). There was no significant correlation between 1,25(OH)2D levels and serum calcium or calcitonin or PTH, although the logarithm of PTH correlated inversely with 1,25(OH)2D levels (r = -0.47, P less than 0.01). Patients who had normal or supranormal 1,25(OH)2D levels despite low GFR tended to have low serum phosphorus values. Serum levels of bone Gla protein (BGP), a biochemical marker for bone metabolism, correlated negatively with 1/serum creatinine (r = -0.39, P less than 0.02) and positively with PTH (r = 0.57, P less than 0.001) and age (r = 0.33, P less than 0.05). Prophylaxis with 1,25(OH)2D should be considered in patients with significantly decreased serum 1,25(OH)2D levels, as seem to occur when serum creatinine is greater than 4.0 mg/dl. However, despite the statistically significant correlation between serum 1,25(OH)2D and 1/serum creatinine, direct measurement should be used to ascertain the serum concentration of 1,25(OH)2D in chronic renal insufficiency.