Positive correlation between serum δ44/42Ca and ALP is in agreement with the recent study of CKD children14; however, they also observed positive association between serum δ44/42Ca and vitamin D, and no correlation or a negative correlation between serum δ44/42Ca and PTH; however, here we observe a negative correlation between serum δ44/42Ca and vitamin D (Fig. 6), and positive between serum δ44/42Ca and PTH (not shown). Here, PTH is linked to chronic kidney disease.