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Difficulty: EasyEndocrinology and Metabolism

Match the following calcium and bone metabolism disorders with their characteristic initial laboratory findings for serum calcium, parathyroid hormone (PTH), and phosphorus.

  • Primary hyperparathyroidismIncreased calcium, increased PTH, decreased phosphorus
  • HypoparathyroidismDecreased calcium, decreased PTH, increased phosphorus
  • Severe Vitamin D deficiencyDecreased calcium, increased PTH, decreased phosphorus
  • Humoral hypercalcemia of malignancyIncreased calcium, decreased PTH, decreased phosphorus

Answer

Primary hyperparathyroidism pairs with increased calcium/increased PTH/decreased phosphorus; Hypoparathyroidism with decreased calcium/decreased PTH/increased phosphorus; Severe Vitamin D deficiency with decreased calcium/increased PTH/decreased phosphorus; Humoral hypercalcemia of malignancy with increased calcium/decreased PTH/decreased phosphorus.
Each condition produces a distinct biochemical profile based on the integrity of the parathyroid-kidney-bone axis. Primary parathyroid disorders show a direct correlation between the gland's output (PTH) and calcium levels, whereas secondary disorders and malignancy show compensatory or suppressed PTH responses.

Step-by-Step Solution

1
Determine the primary physiological defect for each condition.
Identify whether the disorder originates from the parathyroid gland itself (primary excess or deficiency), is a secondary response to calcium deficiency, or is driven by an exogenous-like substance such as PTHrP.
Establishing the origin of the pathology predicts the direction of the PTH level and the resulting electrolyte changes.
2
Apply the physiological effects of PTH and its analogs on serum calcium and phosphorus.
PTH and PTHrP increase serum calcium and decrease serum phosphorus. A lack of PTH does the opposite.
This allows accurate mapping of the clinical condition to the specific laboratory pattern.

Key Concept

Calcium, phosphorus, and PTH homeostasis in parathyroid and bone disorders
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Topics

Endocrinology and Metabolism

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