Case history: An asymptomatic 26-year-old female was found to have hypercalcaemia with an associated normal PTH and vitamin D deficiency on blood tests in primary care. She was referred to the endocrinology clinic for further assessment. There was no history of renal calculi, constipation or fractures. The patient was taking the combined oral contraceptive pill only. There was a family history of hypercalcaemia, with an uncle affected in his 50s and a first cousin in his 20s. Therefore the differential diagnosis included Familial Hypocalciuric Hypercalcaemia (FHH), and Primary Hyperparathyroidism due to Multiple Endocrine Neoplasia type 1 (MEN1).
Investigations: The patient underwent repeat blood tests and 24 hour urinary calcium collection. Due to the possibility of MEN1, fasting gut hormones were also measured.
Results and treatment: Repeat bloods showed a corrected calcium of 2.65 mmol/l, PTH 5.2 pmol/l, phosphate 1.00 mmol/l and a vitamin D 35 nmol/l. Once vitamin D replete, the urinary calcium creatinine clearance ratio was 0.09 supporting a diagnosis of FHH. Fasting gut hormones, at the time of initial assessment showed an isolated raised Chromogranin A of 326 pmol/l which remained raised at 607pmol/l when repeated. Genetic testing identified a mutation in the calcium sensing receptor confirming the diagnosis of FHH. No MEN1 mutation was identified. Despite the confirmed diagnosis of FHH, the Chromogranin A levels remained persistently raised. The patient was referred for a CT abdomen and DOTOTATE scan; both were normal. More detailed testing of Chromogranin A was arranged via Clinical Chemistry. Repeat analysis of serial dilutions on the assay showed that Chromogranin A did not fall linearly with dilution, suggesting assay interference. Furthermore, Chromogranin A levels were normal when repeated on a different assay. No treatment was required for the patient with a confirmed diagnosis of FHH only.
Conclusions and points for discussion: Individuals presenting with hypercalcaemia and elevated gut hormones are often considered to have MEN1, or if no mutation is found, to have a MEN1 phenocopy. Here we present a case with an alternative explanation, removing the need for ongoing follow up. This case also highlights the importance of confirming the diagnosis of primary hyperparathyroidism prior to further investigations for MEN1. Also that assay interference should be considered when results are not in keeping with the clinical picture. Close liaison with Clinical Biochemistry Colleagues can facilitate correct testing with serial dilution assays.