HIGH PREVALENCE OF NORMAL TOTAL CALCIUM AND INTACT PTH IN 60 PATIENTSWITH PROVEN PRIMARY HYPERPARATHYROIDISM - A CHALLENGE TO CURRENT DIAGNOSTIC-CRITERIA

Background: Others have reported a clear distinction between patients with primary hyperparathyroidism (PHPT) and normal subjects using the intact PTH (iPTH) assay. Aim: We reviewed our last 60 surgically prove n cases of PHPT, who had adequate preoperative biochemical assessment, to determine the usefulness of the iPTH assay, ionised calcium and ot her biochemical criteria in differentiating between normal subjects an d patients with PHM: Methods: We conducted a retrospective cross-secti onal study of all patients with surgically proven PHPT who had been re ferred to Sir Charles Gairdner Hospital, Perth, Western Australia for preoperative biochemical assessment. All cases had fasting preoperativ e blood and urine samples collected for ionised calcium, plasma total calcium, albumin, urine calcium excretion, renal phosphate threshold a nd iPTH. Results: Fifty cases had a single or double adenoma and ten h ad hyperplasia. All except one had ionised hypercalcaemia but only 47 (78%) had an elevated corrected total calcium (cCa). Therefore 13 case s (22%) had a normal cCa and five of those patients (8%) had both an i PTH and cCa within the reference range. Forty-nine (82%) had an elevat ed ionised calcium (iCa) and iPTH; the remaining 11 (18%) had an iPTH within the reference range. Of this latter 18%, ten (91%) had a low re nal phosphate threshold and five (45%) had significant renal calcium c onservation: all II cases had at least one abnormality in the renal ha ndling of calcium or phosphate and all normalised their plasma calcium postoperatively (ionised and corrected total calcium). Conclusions: O ne in five patients with proven PHPT have a non-elevated cCa and/or in tact PTH. Ionised calcium should be measured in all suspected cases. A dditional studies of renal calcium and phosphate handling are helpful to establish a diagnosis where any uncertainty exists.