Urinary cyclic AMP. Relation to albumin-corrected serum calcium in healthy persons and patients with primary hyperparathyroidism

In 21 healthy volunteers, mean excretion of cyclic adenosine 3',5' monophosphate (cAMP) in urine was 4.2 +/- 1.0 (S.D.) mumol cAMP/24 hours, 3.0 +/- 1.2 mumol/g creatinine and 3.8 +/- 1.2 mumol/24 hours/100 ml/min renal clearance of creatinine (CCr). An inverse correlation exists between the excretion of cAMP and serum calcium corrected for variations in serum albumin, most clearly demonstrated when cAMP is expressed as mumol/24 hours/100 ml/min of CCr (r=-0.630, p less than 0.01). In 21 patients with operatively verified hyperparathyroidism, the mean urinary excretion of cAMP/24 hours was 5.0 +/- 1.9 mumol uncorrected, 4.8 +/- 1.8 mumol/g creatinine and 6.6 +/- 2.1 mumol/100 ml/min of CCr. The latter two of these parameters differ significantly from the normal group (p less than 0.001), but conceal the fact that many patients with hyperparathyroidism excrete normal amounts of cAMP in the urine, independent of the mode of calculation. However, when cAMP is correlated to albumin-corrected serum calcium, this overlap between hyperparathyroidism and normality disappears completely. The results support the concept that cAMP excretion is influenced to a considerable degree by the biological activity of circulating parathyroid hormone. They also indicate that the simultaneous measurement of cAMP in urine and albumin-corrected calcium in serum is a useful aid in distinguishing hyperparathyroidism from the state of normality.