PTH and secondary hyperparathyroidism: It was remarkable that the parameters of calcium homeostasis before allo-HSCT showed a consistent picture of low to low-normal calcium levels (Fig. 5a), low 25-hydroxyvitamin D (25-OH-D, Fig. 5c), and elevated parathyroid hormone (PTH, i.e., secondary hyperparathyroidism) (Fig. 5d).