Given the findings of this study and the only previous one testing Ca/P in patients with HPT (3), we strongly suggest measuring both serum Ca and P to calculate the Ca/P ratio as the first step in the screening of Ca-P metabolism disorders characterized by hypocalcaemia and hyperphosphatemia, whereas serum PTH is not strictly needed as first-line biochemical investigation. The gene discussed is PTH; the disease is hyperphosphatemia.