Endocrine Abstracts

Normocalcemic primary hyperparathyroidism (nPHPT) is still a poorly understood entity, characterized by increased circulating parathormone (PTH) and normal total and ionic calcium, excluding secondary causes.

Aim: To characterize the cases of nPHPT detected for a whole year from laboratory records of PTH in a tertiary referral centre, with the purpose of assessing a preliminary estimation and describing their main features.

Material and Methods: Retrospective study of a database from the Biochemistry laboratory at “Marqués de Valdecilla” University Hospital (Santander, Spain) including the results of all PTH requests throughout 2018 coming from Primary Care and Hospital departments in Cantabrian health areas I-II (population 420,000).

Results: From 13,201 PTH determinations performed during 2018 in our lab, 4,746 showed an increased iPTH level (>65 pg/ml). Amongst them, 386 samples from 350 patients met the following criteria: normal corrected total calcium (8.1-10.4 mg/dl), normal renal function (eGFR >60 ml/min) and vitamin D sufficiency (>20 g/ml). Then, their electronic records were reviewed and secondary causes of hyperparathyroidism were excluded according to the 4th International Workshop guidelines. Eventually, 31 patients met the diagnostic criteria for nPHPT based on 2 normal values of corrected total calcium, but only 10 had a concomitant determination of ionic calcium, considered as mandatory to confirm nPHPT by the 4th International Workshop. At last, 6 of these 10 patients showed a normal ionic calcium level (1.18-1.30 mmol/l). Regarding the main clinical features of these 6 patients, 2 subjects had been diagnosed of osteopenia/osteoporosis, another one had had previous bone fractures and 3 of them urological findings (only one with confirmed renal lithiasis). In 2 of these 6 patients parathyroid scintigraphy was requested; in one of them a parathyroid adenoma was suggested.

Conclusions: Very few cases of nHPTP were found amongst PTH determinations performed upon suspicion in our health area, suggesting a low prevalence of this entity. Ionic calcium determination is still underused to confirm its diagnosis.