NBME 23 Inorganic phosphorus: decreased;<br />Parathyroid hormone: increased;<br />Calcitriol: decreased (NBME Answers)

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Retired NBME 23 Answers

nbme23/Block 4/Question#3 (reveal difficulty score)
A 33-year-old woman comes to the physician ...
Inorganic phosphorus: decreased;
Parathyroid hormone: increased;
Calcitriol: decreased 🔍 / 📺 / 🌳 / 📖
tags:

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submitted by ∗lfsuarez(160)

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Answer E

Inorganic Phosphorus ; Parathyroid Hormone ; Calcitriol

Decreased ; Increased ; Decreased

This patient is suffering from celiac sprue, which in this case has caused Vitamin D malabsorption and therefore decreased serum calcium. The body will respond to the decreased calcium via secretion of PTH. This will then cause phosphorous wasting to occur in the proximal convoluted tubule.

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kuhnboom Why does Calcitriol not increase with the increased PTH? Wouldn't the increased PTH stimulate the kidneys to make more activated vitamin D. +2

batmane vitamin d malabsorption --> dec calcitriol +6

peridot @kuhnboom Yes, while PTH stimulates the kidneys to make more active vitamin D (calcitriol), you need vitamin D precursors to begin with in order to do that. If you have vitamin D malabsorption, then the activated form won't be high even with high levels of PTH. Therefore, calcitriol is decreased. +

cbreland Also, Vitamin D causes Ca and Phosphate absorption in the intestines. A lack of activated vitamin D would cause more Ca/Phosp wasting +

iwannabedonewiththis Uworld ID: 981 +

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submitted by ∗lumd(4)

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Celiac sprue → fat malabsorption → Decreased ADEK vitamins

Decreased Vit D (Calcitriol) → decreased Ca2+ reabsorption (which 80% is reabsorbed from intestines) → decreased serum Ca2+ → increased PTH → increased renal excretion of Phosphate → decreased serum Phosphorus

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