Fig. 6

Comparison of the Ca (calcium) concentration in acidified urine samples with and without storage. A Passing Bablok regression plot for Ca concentration in acidified urine (x-axis) and acidified urine after storage (y-axis). The thin grey line is the line of identity (y = x) and the thick red line is the line of best fit (the values after acidification are already corrected for the dilution factor). B Bland-Altman difference plot showing agreement of the Ca concentration measurements in native and acidified urine samples. The thin horizontal grey line (0 at the y-axis) is the line of identity, and the thick black line indicates the bias (mean difference between methods), with its confidence intervals as thin dashed lines. The thick dashed horizontal lines are the 95% limits of agreement with their 95% confidence intervals as the thin dashed lines. The mean difference is − 0.23 (− 0.63 to 0.16)*, the Lower Limit of Agreement is − 2.38 (− 3.06 to − 1.70)*, the Upper Limit of Agreement is 1.91 (1.23 to 2.59)*