Challenges in Estimating Renal Function in X-linked Hypophosphatemia Because of Formula Overestimation and FGF23 Effects
Authors' conclusion
eGFR overestimates GFR in XLH, increasing CKD misclassification risk. Annual cystatin C measurement is recommended if CKD is suspected. FGF23 impact on GFR should also be considered in burosumab-treated patients.
Study context
- Population
- Adults with X-linked hypophosphatemia (XLH); 17 females, median age 35 years
- Participants
- 20 adults
- Exposure
- Estimated glomerular filtration rate (eGFR) formulas vs measured GFR
- Outcome
- GFR (mL/min/1.73 m²)
Methodological detailssingle-centre
- Single-centre
Main finding
As reported in the abstract
| Group | Value | Bias | Accuracy |
|---|---|---|---|
| Measured GFR (mGFR) | median 90 (IQR 85–107) mL/min/1.73 m² | ||
| CKD-EPIcreat | 125 (IQR 114–121) | −22 [−29 to −13] | 25% |
| CKD-EPIcyst | 103 | −13 [−19 to −4] | 93% |
Value
Measured GFR (mGFR)median 90 (IQR 85–107) mL/min/1.73 m²
CKD-EPIcreat125 (IQR 114–121)
CKD-EPIcyst103
Bias
Measured GFR (mGFR)— not stated in the abstract
CKD-EPIcreat−22 [−29 to −13]
CKD-EPIcyst−13 [−19 to −4]
Accuracy
Measured GFR (mGFR)— not stated in the abstract
CKD-EPIcreat25%
CKD-EPIcyst93%
- mGFR vs CKD-EPIcreat: P < 0.0001 — mGFR significantly lower
- mGFR vs CKD-EPIcyst: P = 0.01 — mGFR significantly lower
Observational data: associations, not effects.
Further findings
mGFR change after burosumab initiation (XLH subgroup, n=5)
- mGFR decreased (mL/min/1.73 m²)
- 98 to 84
FGF23–eGFR correlation in fibrous dysplasia (pediatric, n=14)
- Moderate correlation
- R = 0.62, P = .02
Renal complications
- Nephrocalcinosis or hypercalciuria
- 0
- Secondary hyperparathyroidism
- 8
Parts of this Brief are withheld: the automatic checks could not confirm them against the abstract.
Original publication
Challenges in Estimating Renal Function in X-linked Hypophosphatemia Because of Formula Overestimation and FGF23 Effects. J Clin Endocrinol Metab. Published 25 August 2025. doi:10.
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