Objective: The diagnosis of primary hyperparathyroidism (PHP) can be difficult in patients with normal plasma calcium or parathyroid hormone (PTH) levels. We perfected a standardized short-time i.v. calcium loading test in healthy controls (HC) and compared the results with those of patients with PHP.
Methods: Sixteen HC received 0.33 mmol/kg calcium gluconate intravenously for 3 h. Plasma calcium and serum PTH levels (assayed with immunoluminescent sandwich methods) were measured before, at the end of the infusion and 3 h later. Results were compared with those of 16 PHP patients.
Results: In HC, basal total plasma calcium (mean ± s.e.m.) was 2.33 ± 0.02 mmol/l. At the end of calcium loading, calcemia reached 3.21 ± 0.05 mmol/l and decreased to 2.94 ± 0.08 mmol/l 3 h later. In PHP patients, basal plasma calcium was 2.54 ± 0.03 mmol/l and reached similar values as in HC during the testing. Basal serum PTH levels were 32.5 ± 3.3 ng/l in HC and 86.9 ± 6.3 ng/l in PHP. At the end of calcium loading, they dropped to 8.8 ± 0.6 ng/l (HC) and to 31.4 ± 4.2 ng/l (PHP). Three hours later, they were 11.6 ± 0.8 and 39.8 ± 4.0 ng/l respectively. There was a cut-off in serum PTH values between the two groups at the end of calcium loading and 3 h later.
Conclusion: The standardized short-time PTH suppression test appears reliable to differentiate healthy subjects from PHP whose serum PTH levels remain >14 and >23 ng/ml respectively at the end of loading and 3 h later. This well-tolerated and easily performed test could be used for the diagnosis of PHP in patients suspected for the disease despite the normality of some basal biological markers.
Dissimilar PTH, Gastrin, and Calcitonin Responses to Oral Calcium and Peptones in Hypocalciuric Hypercalcemia, Primary Hyperparathyroidism, and Normal Subjects: A Useful Tool for Differential Diagnosis