[Clinical usefulness of the determination of fibroblast growth factor 23 in the evaluation of patients with osteomalacia].

Background And Objective: The aim of the present study was to analyze the usefulness of the determination of fibroblast growth factor 23 (FGF23), a regulatory hormone of phosphate metabolism, in the evaluation of patients with osteomalacia of different causes.

Patients And Method: Seventeen patients with osteomalacia were included: 12 hypophosphatemic osteomalacia (by several causes), 4 vitamin D-deficiency osteomalacia and one with hypophosphatasia. Plasma C-terminal FGF23 was determined in all patients.

Results: FGF23 levels were increased in 6/12 (50%) of patients with hypophosphatemic osteomalacia (2 X-linked, one autosomal dominant, one related HIV therapy and 2 not elucidated). No patient with vitamin D-deficiency osteomalacia or hypophosphatasia presented increased FGF23 levels.

Conclusion: The determination of FGF23 could be useful in the evaluation of the different types of hypophosphatemic osteomalacia and also in the identification of their associated etiopathogenic mechanisms. Thus, depending on the cause, 50% of the patients with hypophosphatemic osteomalacia showed increased FGF23 values, whereas in vitamin D-deficiency osteomalacia and in hypophosphatasia FGF23 levels were normal.