Interpretation of laboratory tests in adults with suspected osteomalacia

PTH: parathyroid hormone; 25(OH)D: 25-hydroxyvitamin D; eGFR: estimated glomerular filtration rate; FGF23: fibroblast growth factor 23.

* A diagnosis of hypophosphatasia is supported by elevated levels of plasma pyridoxal 5'-phosphate and urine phosphoethanolamine and can be confirmed through genetic testing.

¶ PTH is typically normal in most renal phosphate wasting disorders but may be mildly elevated. Secondary hyperparathyroidism may be evident in X-linked hypophosphatemia. The hereditary phosphate wasting disorders autosomal dominant hypophosphatemia, hypophosphatemic rickets with hypercalciuria, and X-linked hypophosphatemia may present initially in adulthood. An elevated FGF23 level supports tumor-induced osteomalacia as the underlying etiology, which warrants efforts to localize the tumor. In adults, Fanconi syndrome is usually acquired and most often due to multiple myeloma or medications.

Δ Mineralization inhibitors include fluoride, aluminum, and heavy metals. Disorders of bone matrix include axial osteomalacia and fibrogenesis imperfecta. In these rare disorders, all laboratory results are usually normal, and differentiating between osteomalacia and osteoporosis may require bone biopsy.