Lack of Correlation between Calcium Intake and Serum Calcium Levels in Stable Haemodialysis Subjects

Abstract

Background: The relationship between calcium intake and serum calcium level in hemodialysis patients is poorly understood. Methods: We quantify total oral calcium intake using detailed 7-day food diaries with 294 patient days of observation in 42 stable, non-diabetic hemodialysis subjects. Results: Mean (SD) albumin-corrected serum calcium was 9.84 mg/dl (0.8). The albumin-corrected serum calcium was low (<8.4 mg/dl) in 2 patients, low-normal (8.4–9.49) in 9 patients, high-normal (9.5–10.2) in 18 patients and high (>10.2) in 13 patients. Mean (SD) total (diet plus binder) oral calcium intake was 1996 mg/day (1,020); 16 patients (38%) had a total calcium intake >2,000 mg/day. Calcium intake and serum calcium were poorly correlated (Spearman rank method), r = 0.14, p = 0.39. Median calcium intakes were similar in those with normal (1,990 mg/day), high-normal (1,926 mg/day) and high calcium groups (1,713 mg/day), p = 0.73 (Kruskal-Wallis), p = 0.29 (linear test for trend). Forty-one percent (11/27) of patients who had serum calcium in the normal range had a calcium intake greater than 2 g/day, while 11.5% had a calcium intake greater than 3 g/day. In subjects with a parathyroid hormone (PTH) concentration <300 pg/ml (n = 20), the correlation between calcium intake and either uncorrected serum calcium or albumin-corrected serum calcium was stronger, r = 0.45, p = 0.05 and r = 0.38, p = 0.10, respectively, though there remained wide variability in calcium intake. Conclusion: Serum calcium is not a reliable indicator of calcium intake, especially at PTH ≥300 pg/ml. An excessive calcium intake may coexist with a normal serum calcium level.