Endocrine Abstracts (2019) 65 P122 | DOI: 10.1530/endoabs.65.P122

Differential diagnosis of pseudohypercalcaemia by measurement of ionised calcium

Ffion Wood1,2, Katerina Jonathan1,3, Catrin Searell1,2, Alex Kraus1,4 & Tony Wilton1,3

1Ysbyty Gwynedd, Bangor, UK; 2Department of Clinical Chemistry, Bangor, UK; 3Department of Endocrinology, Bangor, UK; 4Department of Radiology, Bangor, UK

Pseudohypercalcaemia is defined as an elevated total calcium level coincidental with a normal ionised calcium level. This rare phenomenon occurs in monoclonal gammopathy of unknown significance (MGUS). We report two cases of MGUS and a case of atopy with grossly elevated IgE levels exhibiting the phenomenon.

Case 1: 31 year old female with MGUS, hypercalcaemia and normal parathyroid (PTH) levels. Parathyroid imaging normal. Consensus diagnosis of primary hyperparathyroidism. At surgery two apparently normal parathyroid glands removed but histology normal. Calcium and PTH levels unchanged but ionised calcium normal confirming pseudohypercalcaemia.

Case 2: 74 year old male with MGUS, hypercalcaemia and normal PTH levels. Imaging normal. Diagnosed as primary hyperparathyroidism and surgery planned. The finding of a normal ionised calcium level avoided surgery.

Case 3: 61 year old male diagnosed as having primary hyperparathyroidism on the basis of hypercalcaemia and normal PTH levels. Grossly elevated IgE levels and normal ionised calcium obviated imaging studies and surgical intervention. These cases demonstrate the utility of ionised calcium measurement in diagnosing pseudohypocalcaemia. We believe that this to be the first report of pseudohypercalcaemia due to high levels of a normal immunoglobulin.

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