USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the typical presentation of hypoparathyroidism?

1. Increased serum calcium

2. Decreased ionized calcium levels

3. Decreased serum phosphorus

4. Hypertension

The correct answer is: Decreased ionized calcium levels

Hypoparathyroidism is characterized by a deficiency of parathyroid hormone (PTH), which plays a crucial role in regulating calcium and phosphorus levels in the blood. In hypoparathyroidism, the lack of PTH leads to a decrease in bone resorption and renal reabsorption of calcium, resulting in low serum levels of ionized calcium. In addition to decreased ionized calcium levels, patients with hypoparathyroidism may experience symptoms such as tingling, muscle cramps, and seizures due to low calcium levels. Since PTH typically promotes calcium release from bones and renal tubular reabsorption, its deficiency directly contributes to the observed decrease in serum calcium. Therefore, the typical presentation of hypoparathyroidism includes low levels of both total and ionized calcium in the blood, establishing option B as the correct choice. Other conditions or disruptions in calcium homeostasis would lead to different findings: increased serum calcium is typically seen in conditions like hyperparathyroidism, decreased serum phosphorus is often observed in hyperparathyroidism or in states of excessive vitamin D, and hypertension is not a primary feature of hypoparathyroidism. This context highlights the specificity of decreased ionized calcium levels in accurately representing the typical presentation of hypop