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. 2021 Jan;184(1):K7-K10.
doi: 10.1530/EJE-20-0634.

Normocalcaemic hyperparathyroidism and primary hyperparathyroidism: least significant change for adjusted serum calcium

Marian Schini  1 , Richard Jacques  2 , Eleanor Oakes  3 , Nicola Peel  3 , Jennifer S Walsh  1 , Richard Eastell  1
Affiliations

Normocalcaemic hyperparathyroidism and primary hyperparathyroidism: least significant change for adjusted serum calcium

Marian Schini et al. Eur J Endocrinol. 2021 Jan.

Abstract

Introduction: The least significant change (LSC) is a term used in individuals in order to evaluate whether one measurement has changed significantly from the previous one. It is widely used when assessing bone mineral density (BMD) scans. To the best of our knowledge, there no such estimate available in the literature for patients with disorders of calcium metabolism. Our aim was to provide an estimate of the least significant change for albumin-adjusted calcium in patients with normocalcaemic hyperparathyroidism (NPHPT) and primary hyperparathyroidism (PHPT).

Methods: We used the within-subject standard deviatio calculated in a population of NPHPT and PHPT patients and multiplied it by 2.77.

Results: The LSC for NPHPT and PHPT were found to be 0.25 and 0.24 mmol/L, respectively (1.00 and 0.96 mg/dL). In clinical practice, the value of 0.25 mmol/L could be used.

Discussion: The least significant change given, could be used in two ways in these patients. First, it gives a range to which values are expected. This can provide some reassurance for the patient and the physician in cases of intermittent hypercalcaemia. Moreover, it can be a marker of whether an individual has an actual significant change of his calcium after parathyroid surgery.

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Figures

Figure 1
Figure 1
The follow up measurements from a patient with normocalcaemic hyperparathyroidism (NPHPT, left) and primary hyperparathyroidism (PHPT, right), both having intermittent hypercalcaemia yet all results falling with the LSC. The dashed lines represent the reference interval for calcium. The grey areas represent the least significant change (LSC: 0.25 and 0.24 mmol/L for NPHPT and PHPT, respectively); these are given around the first available measurement of calcium. Adj.Ca, adjusted calcium.
Figure 2
Figure 2
The follow up measurements from a patient with primary hyperparathyroidism patient (PHPT) who had parathyroid surgery (vertical dotted line). The dashed lines represent the reference interval for calcium. The grey area represents the least significant change (LSC: 0.24 mmol/L); this is given around the first available measurement of calcium. Adj.Ca, adjusted calcium. It can be seen that the postoperative calcium measurements all change by more than the LSC.
See this image and copyright information in PMC

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