Biphasic relationship between the severity of abdominal aortic calcification with the phosphaturic response to FGF23. Linear regression (Gray line) and non parametric regression (Black, continuous lines) depicting the relationships between the ratio of FEP/FGF23 (in logarithmic scale (base 2): log2(FEP/FGF23)), in the X axis, with the Kauppila Index (Y axis). The softer continuous lanes mark the dispersion from the mean fit (see Methods for specifics). The box plot below the X axis shows that the cut-off point FEP/FGF23 = 1/3.9 coincides with the median for the log2(FEP/FGF23) in our patient population. Note that the cut-off point FEP/FGF23 = 1/3.9 also marks an inflexion point for quite distinct average changes for KI with changes in FEP/FGF23 ratios above and below the cut-off: No change in KI for FEP/FGF23 ratios above the cut off; Parallel increases in KI with decreases in FEP/FGF23 ratios below the cut-off. Note in the X axis, the FEP/FGF23 ratios corresponding to the values of log2(FEP/FGF23). The Box plot for KI distribution in our patients is depicted to the left of the Y axes.