Endocrine Abstracts

Introduction: Evidence suggests that ionised calcium (iCa) and not total calcium is the physiologically relevant blood calcium component. Most blood gas (BG) analysers calculate iCa, but this is often ignored. We report our findings from a retrospective audit in medical in-patients and the potential benefit of this underused resource.

Methods: A retrospective audit of admissions to two general medical/endocrine wards during January and February 2016. Database included arterial or venous BG values, PTH, vitamin D, serum calcium, proton pump inhibitor (PPI). Clinical information was obtained from e-discharge letters.

Results: Of 270 patients admitted, 137 had one or more BG. 60 of the 137 (43.8%) had abnormal iCa; 19 (32%) had hypercalcemia (iCa>1.27 mmolL-1) on admission, whilst 41 (68%) had hypocalcaemia (iCa<1.15 mmolL-1). Of the 60 abnormal iCa, only 29 (48%) had laboratory calcium checked during admission. There was a significant correlation between iCa and adjusted Calcium (aCa) estimated in the lab (R=0.41, P=0.003). Proportion of patients with low, normal and high iCa on admission vs. discharge calcium (iCa or aCa) was 33%, 47%, 20% vs 14%, 74%, 12% (P=0.030). Vitamin D/PTH estimation was undertaken in 7.3% of those with hypocalcaemia and 10% of those with hypercalcaemia. Magnesium was checked in 9 patients (22%) with hypocalcaemia. PPI use was observed in 42% of those with hypocalcaemia.

Discussion: iCa available in BG results continues to be overlooked. Three-quarters had mild hypocalcaemia; however this was acted upon or repeated in only half the cases. It is important that medical teams are encouraged to review the iCa performed on initial ABG and any follow up tests performed appropriately. Chronic PPI use can cause hypomagnesemia and consequent hypocalcaemia. Eleven patients in our study with unresolved hypocalcaemia were on PPI. We recommend all patients on PPIs with hypocalcaemia must have their magnesium checked.