Urinary cyclic adenosine monophosphate discriminates subsets of patients with osteoporosis1
To assess the biologic activity of the parathyroid hormone in osteoporosis, 32 patients with radiologic and clinical evidence of this disease were studied. Measurements of urinary cyclic adenosine monophosphate (cAMP), serum calcitriol (1,25 dihydroxyvitamin D), calcium, phosphorus, albumin, creatinine, and estimated glomerular filtration were obtained. The high cAMP group averaged 5.68 μmol cAMP/g (SEM, 0.35) and the low cAMP group, 2.89 μmol cAMP/g (SEM, 0.22) of creatinine. Mean urinary calcium levels were lower (P < 0.05) in the high cAMP group (120 ± 16 versus 288 ± 54 mg/d). Seventy percent of the values from the high cAMP group were below 150 mg/d and averaged 88 mg (range, 36–127). About 70% of the patients with the low cAMP values excreted 368 mg daily (range, 170–700). Although both groups had similar levels of serum calcitriol, almost 70% of the patients had values below the reference limit for the mean; more than 80% of this group were excreting less than 150 mg of calcium daily. Because urinary cAMP levels of patients form a separate distribution from those of young normals, patients can be divided into groups with low or high cAMP values displaying different patterns of calcium excretion. Increased levels of cAMP may represent enhanced parathyroid gland secretory activity due to a deficiency of dietary calcium or to poor absorption from inadequate production of vitamin D.