Fluid & Electrolyte Q 101

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Etiologies associated with hypocalcemia may include all of the following except:

  

    A. Renal failure

    B. Inadequate intake calcium

    C. Metastatic bone lesions

    D. Vitamin D deficiency

    

    

Correct Answer: C. Metastatic bone lesions

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Metastatic bone lesions are associated with hypercalcemia due to accelerated bone metabolism and release of calcium into the serum. Although more common in adults than pediatric patients, the next important etiology to consider is malignancy. Renal carcinomas, leukemias, lymphomas, and rhabdomyosarcoma can be associated with elevated calcium levels mediated by the action of PTH-related peptides. Renal failure, inadequate calcium intake, and vitamin D deficiency may cause hypocalcemia.

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Option A: CKD leads to impaired phosphate excretion which drives PTH secretion and can cause secondary hyperparathyroidism. However, due to impaired Vitamin D metabolism and high phosphorus level, the serum calcium remains low despite the high PTH.

Option B: Serum calcium is normally bound to proteins in the blood most prominently albumin and therefore low albumin states can give a falsely low total serum calcium level. Ionized calcium level is usually normal in these states and thus a correction of adding 0.8 mg/dL to serum calcium level is usually recommended for every 1gm drop in serum albumin below normal (4 gm/dL)

Option D: Absolute or relative Vitamin D deficiency includes lack of active metabolite of vitamin D due to inadequate sun exposure or liver disease or kidney disease. Also, included in this category are familial causes of vitamin D resistance.

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