Biochemical diagnosis of primary hyperparathyroidism: Analysis of the sensitivity of total and ionized calcium in combination with PTH

ObjectivesTo investigate the accuracy of the biochemical diagnosis of primary hyperparathyroidism (pHPT) in a consecutive series of patients with operatively verified disease.Design and subjectsFour hundred thirty-six patients with pHPT, 340 women and 96 men, were reviewed. Biochemical variables, including total calcium (Ca), ionized calcium (Cai) and PTH were analyzed and registered in a prospective database.ResultsIn the subgroup of patients with more mild hypercalcemia (Ca below 2.70 mmol/L) the correlation between Ca and Cai was poor. 19 respectively 18 patients had preoperatively a Ca respectively Cai level within the reference range. Further 35 patients had preoperatively a normal level of PTH. The diagnostic sensitivities, in detecting pHPT, for Ca, Cai and the combination of Ca and Cai were 96%, 96% and 99%.ConclusionIf calcium and ionized calcium are not used in the diagnostic workup of pHPT some 4% of the patients will be overlooked.We recommend analyzing both Ca and Cai in the diagnostic workup of pHPT.