Assessment of adenosine 3',5'-monophosphate excretion and an oral calcium tolerance test in the diagnosis of mild primary hyperparathyroidism.

An oral calcium tolerance test was administered to 22 hyperparathyroid patients and 162 normal subjects to determine its value in the diagnosis of mild primary hyperparathyroidism. Basal urinary excretion of calcium was higher in patients [0.217 mg/100 ml glomerular filtrate (GF)] than in normal subjects (0.090 mg/100 ml GF), but there was 50% overlap between the two groups. Phosphorus excretion, expressed as the ratio of the maximal tubular reabsorption of phosphorus to the glomerular filtration rate, was lower in patients (2.77) than in normal subjects (3.7), but 38% of the patients fell within the normal range. Urinary excretion of total cAMP also failed to separate hyperparathyroid patients from normal subjects [5.8 +/- 0.32 (+/- SEM) nmol/100 ml GF in patients vs. 3.41 +/- 0.11 in normal subjects]. Determination of nephrogenous cAMP failed to increase the utility of cAMP as a predictor of hyperparathyroidism. In response to oral calcium, the elevation in serum calcium concentration was the same in both groups. The rise in urinary calcium was greater in patients, but showed 77% overlap with that in normal subjects. Conversely, serum immunoreactive PTH, measured with a midregion-specific RIA, was elevated in 90% of the patients. Some normal subjects also had high levels of PTH, but none of these had hypercalcemia. We conclude that the oral calcium tolerance test and measurement of urinary cAMP do not adequately distinguish hyperparathyroid patients from normal subjects. In the absence of renal insufficiency, the combination of hypercalcemia and elevated serum PTH concentration most accurately predicts the diagnosis of primary hyperparathyroidism.