Influence of Calcium Infusion on Urinary Cyclic AMP and Phosphate in Hyperparathyroidism

Abstract

Urinary cyclic AMP (CAMP) and phosphate were measured before and after calcium infusion in 12 patients with operatively verified primary hyperparathyroidism (PHP) and in 12 healthy persons. In normal subjects infusion of calcium caused a reduction in urinary cAMP directly correlated to the preinfusion values and inversely correlated to the serum calcium concentration determined as albumin-corrected serum calcium. In normal subjects with high normal albumin-corrected serum calcium the infusion of calcium caused no or only a small depression in the urinary excretion of CAMP. Changes in phosphate excretion were not correlated to the calcium concentration. Four of the 12 hyperparathyroid patients showed normal relative suppression in urinary cAMP after the infusion of calcium, and 5 had normal suppression of phosphate excretion. It is concluded that some patients with PHP retain calcium-sensitive secretion of PTH, and that the classical calcium infusion test is of doubtful value in the diagnosis of PHP. Kev words: urinary CAMP, phosphate, i.v. calcium. Acta Med Scand 210: 15, 1981.Measurement of urinary cyclic adenosine 3'5'monophosphate (CAMP) has been established as useful in the diagnosis of primary hyperparathyroidism (PHP) (10, 12). In normal man, cAMP excretion is inversely correlated to the concentration of serum calcium, whereas hyperparathyroid patients excrete pore cAMP than one would expect from this interrelation (13, 17). The diagnostic value of measurement of urinary cAMP is therefore improved when analysed as a function of serum calcium.Howard et al. (8) introduced the calcium infusion or suppression test, assuming that serum calcium levels in PHP were unable to affect parathyroid hormone (PTH) secretion (theory of parathyroid autonomy), and observed accordingly that calcium infusion decreased phosphate excretion in normal controls, whereas PHP patients were nonor hyposuppressible. This outcome would be expected under conditions of hypercalcemia, because hypercalcemic patients have to be either primary hyperor secondary hypoparathyroid.Murray et al. ( I 1) observed that PTH secretion in PHP was not always autonomous, but frequently varied with induced changes in serum calcium concentrations. In spite of these findings, Pak and Bartter (IS) suggested that calcium infusion is of valtie in detecting hyperparathyroidism in normocalcemic or doubtly hypercalcemic patients with nephrolithiasis of calcium phosphate origin. Their patients were classified according to the total serum calcium levels estimated by a routine procedure.The present study explores that calcium-induced changes in urinary cAMP and phosphate in normal subjects and in PHP patients with borderline or increased levels of total serum calcium as determined by a routine technique, and evaluates the diagnostic usefulness of calcium infusion in discrimination between PHP and normality. SUBJECTSThe study comprised 12 healthy volunteers, 3 males and 9 females aged 17-46 years (mean 24), and 12 patients with PHP, 6 males and 6 females aged 21-69 ye...