Association between admission serum calcium and hemoglobin in older patients with hip fracture: a cross-sectional study.

PURPOSE Serum calcium ion is an essential cofactor in the coagulation cascade, and low calcium concentration is associated with more bleeding in many diseases. This study aimed to describe the prevalence of hypocalcaemia, and investigate the correlation between calcium and hemoglobin (Hb) level in older patients with hip fracture. METHODS From our established hip fracture database, patients were consecutively included between January 2014 and December 2020. Serum calcium concentration was corrected for albumin level, and hypocalcaemia was defined as corrected calcium below the lower limit of reference range (< 2.11 mmol/L), and further sub-grouped into mild hypocalcaemia (1.90-2.11 mmol/L) and severe hypocalcaemia (< 1.90 mmol/L). Pearson correlation, scatter plots and partial correlation analyses were performed to evaluate the associations between various factors and Hb level. RESULTS A total of 1032 older patients with hip fracture were finally included (mean age 79.2 years, 66.0% female). At admission, the mean serum corrected calcium and Hb levels were 2.14 mmol/L and 11.0 g/dL. Overall, the prevalence of hypocalcaemia and anemia were 39.5% and 71.6%, respectively. After adjusting for all variables, low serum calcium concentration was positively associated with low Hb level in the total study (partial correlation r = 0.13, P < 0.001), as well as in patients with femur neck fracture (partial correlation r = 0.16, P = 0.001) and intertrochanteric fracture (partial correlation r = 0.13, P = 0.003). CONCLUSION Hypocalcaemia was common in older patients with hip fracture, and independently and positively associated with low Hb level. Further study on causal relationship between calcium and Hb level in older patients with hip fracture is necessary.