Arsenazo 3

Serum levels of total calcium were determined by Arsenazo III colorimetry (Beckman Coulter, Brea, America) using fresh samples on the day of collection. This assay has a functional sensitivity of 0.01 mmol/L. The mean coefficient of variation was 0.57%. Albumin levels were tested by the bromocresol green colorimetric method (Beckman Coulter, Brea, America), and the mean coefficient of variation was 1.30%. Serum levels of total calcium and albumin were measured using the same method in both the 2007 and 2012 surveys. The levels of albumin-corrected calcium were calculated according to the following formula (11 (link)): albumin-corrected calcium (mmol/L) = measured total calcium (mmol/L) + 0.02 × [40 – albumin (g/L)].

The assessment of serum calcium was routinely conducted for all of the enrolled patients within 24 h after admission. Levels of serum calcium were measured by Arsenazo III colorimetry (Beckman Coulter, Brea, America) using fresh samples, which had a functional sensitivity of 0.01 mmol/L. It was unadjusted for serum albumin and the reference interval of serum calcium for our laboratory ranged from 2.11 to 2.52 mmol/L. Hypocalcemia was defined as a serum calcium level ≤ 2.12 mmol/L [17 (link)].