Table 1.
Pre-operative results of phosphate, calcium and bone-related biochemistry.
| Study | Interpretation | Pre-operative result | Normal range (units) |
|---|---|---|---|
| Serum phosphate | Low | 0.47 | 0.8–1.5 (mmol/L) |
| Renal tubular phosphate excretion | High | 51.05 | 85–95 (%) |
| Serum corrected calcium | Normal | 2.23 | 2.15–2.55 (mmol/L) |
| Serum magnesium | Normal | 0.82 | 0.70–1.10 (mmol/L) |
| Serum PTH | Normal | 5.8 | 1.6–6.9 (pmol/L) |
| Serum 25-hydroxy-vitD3 | Normal | 57 | 50–140 (nmol/L) |
| Serum 1–25-dihydroxy-vitD3 | Low | 27 | 60–210 (pmol/L) |
| Serum bone-specific ALP | High | 106 | 5.5–24.6 (μg/L) |
| Urine DPD/creatinine ratio | High | 15.8 | 2.3–5.4 (μmol/mmol) |
| Serum intact FGF-23 | High | 140 | 10–54 (ng/L) |
PTH = parathyroid hormone; vitD3 = vitamin D3; ALP = alkaline phosphatase; DPD = deoxypyridinoline; FGF-23 = fibroblast growth factor-23
Pre-operative results highlight consequences of elevated circulating FGF-23 levels: serum hypophosphataemia due to excess renal tubular phosphate excretion and suppressed 1-25-dihydroxy-vitD3, with associated accelerated bone turnover (elevated bone-specific ALP and urine DPD/creatinine ratio).
Hypomagnasaemia and hyperparathyroidism were excluded as causes of hypophosphataemia.