On the Diagnosis of So‐called Normocalcaemic Hyperparathyroidism

Abstract

ABSTRACT With the purpose of evaluating their relative efficiency in detecting hypercalcaemia in hyperparathyroidism (HPT), simultaneous determinations have been carried out of serum total calcium (TOCa) in a routine laboratory and serum TOCa, ultrafiltrable (UFCa) and ionized calcium (Ca++) in a research laboratory. All 69 patients in this series, except one, were hypercalcaemic as judged from Ca++ and/or UFCa, and the diagnosis was verified operatively in all. The prevalence of normocalcaemic HPT was 48% as judged from routine TOCa, 14% from research TOCa, 7% from UFCa and 0–1% from Ca++. Thirty‐three patients had normocalcaemic HPT as evaluated by the routine TOCa technic, but in as many as 23 hereof (70%) this “normocalcaemia” appeared to be due to inappropriate normal standards or laboratory errors. Of the remaining 10 patients (30%), being truly normocalcaemic, two had serum calcium‐lowering conditions, while eight appeared to have no other explanation for their normocalcaemia than a modest degree of HPT. Determinations of UFCa and Ca++ were essential in the detection of minimal degrees of hypercalcaemia in nine of the 10 cases of true normocalcaemic HPT and valuable for the establishment of a firm diagnosis in a further 10 cases of borderline hypercalcaemia. Percentages of 10–20 and 0.2, respectively, are given as approximate figures for the prevalences of normocalcaemic patients in HPT, and of HPT, normocalcaemic+hypercalcaemic, in adults attending out‐patient clinics.