Adjustment of total plasma calcium for albumin concentrations avoids overdiagnosis of hypocalcemia in geriatric patients

BACKGROUND: Calcium is critically involved in bone metabolism and stability, nerve excitability and intercellular signal transduction. METHODS: In this retrospective study, calcium plasma concentrations of all patients treated in 2018 at our institution were evaluated. As approximately 50% of the plasma calcium is bound to plasma proteins, in particular albumin, additionally the respective plasma albumin concentration was determined and the albumin-corrected calcium plasma concentration was estimated. RESULTS: In 1246 of 1721 cases the plasma calcium concentration on admission was normal (2.15-2.55 mmol/l), in 421 cases hypocalcemia (< 2.15 mmol/l) and in 38 cases hypercalcemia (> 2.55 mmol/l) were detected. In 1226 of 1543 cases (79.5%) hypoalbuminemia was noted. After correction of the plasma calcium levels for plasma albumin by the modified Payne equation, the corrected plasma calcium was normal in 1272 cases (73.9%), decreased in 15 cases (0.9%), and elevated in 256 cases (14.9%). The frequency of hypercalcemia > 2.8 mmol/l requiring rapid clinical interventions without correction for plasma albumin was 6 of 1705 patients (0.4%), after correction for albumin 24 of 1543 patients (1.6%). In logistic regression analysis, higher albumin was strongly associated with a decreased mortality (odds ratio, OR = 0.88, 95% confidence interval, CI 0.83-0.94, p < 0.001), whereas the plasma calcium concentration had no independent influence on mortality. CONCLUSION: Without correction for plasma albumin, approximately 25% of the patients were hypocalcemic on admission. After correction for plasma albumin, this rate fell to < 1%. We suggest that the determination of plasma albumin should be included in the clinical routine on admission in all geriatric patients.