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Maya Styner, Nichole Korpi-Steiner, Commentary, Clinical Chemistry, Volume 64, Issue 1, 1 January 2018, Pages 51–52, https://doi.org/10.1373/clinchem.2017.281865
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This case of postgastric bypass osteomalacia, secondary hyperparathyroidism, and resulting pelvic fractures highlights important concepts in bone fragility, as well as the significance of the oft-ordered and poorly understood 25-OH vitamin D. Obesity is well-recognized to be protective against pelvic and hip fractures (1). Although gastric bypass increases the risk for potential bone loss, it is intriguing that this patient had pelvic fractures years after she regained most of her weight, suggesting mechanical unloading was unlikely a major contributor.
The Institute of Medicine recommends a 25-OH vitamin D ≥20 ng/mL as generally adequate for bone health. Post-gastric-bypass patients may require 25-OH vitamin D concentrations much higher than 20 ng/mL to permit appropriate absorption of calcium and phosphorus in the gut. Notably, most post-bypass patients who maintain 25-OH vitamin D concentrations around 30 ng/mL fail to demonstrate a prominent increase in parathyroid hormone (PTH), emphasizing the uniqueness of this case regarding PTH concentrations. Although the iron concentration was low, other nutrients' concentration, including B12 concentration, was normal, underscoring a need to maintain a high suspicion for calcium malabsorption and secondary increase of PTH in such patients.
