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Difficulty: EasyEndocrinology and Metabolism

Match the following serum calcium and intact parathyroid hormone (PTH) laboratory profiles to their most likely underlying pathophysiologic diagnosis.

  • Elevated serum calcium and elevated intact PTHPrimary hyperparathyroidism
  • Decreased serum calcium and elevated intact PTHVitamin D deficiency
  • Elevated serum calcium and suppressed intact PTHHumoral hypercalcemia of malignancy
  • Decreased serum calcium and suppressed intact PTHIatrogenic parathyroidectomy

Answer

Elevated Ca/Elevated PTH matches Primary hyperparathyroidism. Decreased Ca/Elevated PTH matches Vitamin D deficiency. Elevated Ca/Suppressed PTH matches Humoral hypercalcemia of malignancy. Decreased Ca/Suppressed PTH matches Iatrogenic parathyroidectomy.
The parathyroid glands maintain calcium homeostasis through a direct negative feedback loop. Normal physiology dictates an inverse relationship: high calcium suppresses PTH, and low calcium stimulates PTH (secondary disorders). A direct relationship (both high or both low) indicates a primary parathyroid disorder.

Step-by-Step Solution

1
Evaluate the serum calcium level in the provided profile.
Determines whether the clinical state is characterized by hypercalcemia or hypocalcemia.
Calcium is the primary regulated variable in this endocrine loop, driving the downstream hormonal response.
2
Evaluate the intact PTH level in the context of the calcium abnormality.
Identifies if the PTH response is appropriate (compensatory) or inappropriate (primary pathology).
An intact negative feedback loop will show PTH moving in the opposite direction of calcium. If PTH moves in the same direction, the parathyroid gland is the source of the pathology.

Key Concept

Calcium and Parathyroid Hormone (PTH) Homeostasis and Feedback Loop
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Topics

Endocrinology and Metabolism

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