Recognition of the Oral Calcium Loading Test in the Setting of Normocalcemic Hypercalcemia: A Case Series Report

Context: Normocalcemic hyperparathyroidism is characterized by the persistence of normal serum calcium levels and elevated intact parathyroid hormone (PTH) values, after the exclusion of other secondary hyperparathyroidism causes. Patients with this condition can present with progressive complications, such as the conversion to primary hyperparathyroidism, as well as the development of osteoporosis and nephrolithiasis. The diagnosis can be challenging due to a vast number of issues including the differentiation between normocalcemic hypercalcemia and primary hyperparathyroidism, since both have similar biochemical findings. The calcium loading test was employed in this study to determine its diagnostic value in the early delimitation of both conditions.

Case Description:

Objective: The aim of the study is to describe the clinical value of the oral calcium loading test in the distinction of normocalcemic hyperparathyroidism due to an inadequate calcium intake or absorption versus primary hyperparathyroidism.

Design: A retrospective chart review of three patients diagnosed with primary hyperparathyroidism who underwent oral calcium loading test was conducted.

Results: We described two patients with malabsorption syndrome and one patient with inadequate calcium dietary intake, who were undergoing diagnostic assessment for primary hyperparathyroidism intervention. Case 1 was a 64-year-old female with 3 years follow up due to asymptomatic primary hyperparathyroidism. Case 2 was a 57-year-old female with right inferior parathyroid hyperplasia resection in 2005 with normocalcemic hyperparathyroidism since the intervention, and case 3 was a 71-year-old male patient diagnosed with primary hyperparathyroidism who was not convinced of a surgical approach. Patients were on a series of follow ups due to repetitive biochemical values and no symptoms. Their oral calcium loading test results showed a substantial decrease in iPTH after 1g of elemental calcium administration. All the patients were referred for gastroenterology and nutritional evaluation. The first two cases were eventually diagnosed with IBS, and after appropriate treatment, laboratory levels were within reference. The last patient increased calcium derived products in his diet, and iPTH levels normalized as well.

Conclusion:

The oral calcium loading test is a particularly valuable tool in the evaluation of patients with biochemical findings consistent with normocalcemic hyperparathyroidism. It could differentiate gastrointestinal and nutritional problems from native parathyroid changes, reducing concurrent clinical follow ups and unnecessary imaging and surgical intervention assessments modalities.