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Difficulty: MediumEndocrinology and Metabolism

Match each laboratory profile of serum calcium, phosphorus, and intact parathyroid hormone (PTH) to the most likely underlying clinical diagnosis.

  • Elevated serum calcium, decreased serum phosphorus, elevated intact PTHPrimary hyperparathyroidism
  • Elevated serum calcium, decreased serum phosphorus, suppressed intact PTHHypercalcemia of malignancy (PTHrP-mediated)
  • Decreased serum calcium, elevated serum phosphorus, suppressed intact PTHPrimary hypoparathyroidism
  • Decreased serum calcium, decreased serum phosphorus, elevated intact PTHSevere Vitamin D deficiency

Answer

Properly align each laboratory derangement based on the physiological feedback loop between calcium and intact PTH.
Matching these diagnostic patterns correctly relies on understanding standard endocrine feedback loops. Primary pathologies (primary hyper/hypoparathyroidism) feature an inappropriate PTH level for the corresponding calcium state. Secondary responses (like Vitamin D deficiency or PTHrP production) show appropriate intact PTH suppression or elevation in response to the primary calcium disturbance.

Step-by-Step Solution

1
Analyze the serum calcium level and the corresponding intact PTH response.
Identifies if the PTH level is appropriately suppressed, appropriately elevated, or pathologically driving the calcium derangement.
Intact PTH should normally decrease when calcium is high and increase when calcium is low.
2
Examine the serum phosphorus level in relation to the PTH activity.
Confirms the expected renal effects of PTH or PTHrP, which generally wastes phosphorus.
High PTH activity (endogenous or ectopic) leads to hypophosphatemia, while low PTH activity leads to hyperphosphatemia.

Key Concept

Calcium, Phosphorus, and PTH Homeostasis
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Topics

Endocrinology and Metabolism

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