FGF23 and X-linked hypophosphatemia: • XLH has a broad differential-diagnosis. A correct diagnosis relies on the integration of clinical, radiological, biochemical and genetic findings.• We recommend a multimodal work-up of suspected XLH by an experienced clinician to exclude other diseases.• Pre-analytical and analytical challenges in the interpretation of plasma phosphate, alkaline phosphatase (ALP), phosphaturia, calciuria, 1,25-dihydroxyvitamin D and FGF23 should be taken into account.