Orthopaedic Nurses Certification Board (ONCB) Metabolic/Inflammatory/Tumors Practice Exam

What laboratory finding is expected in a patient with hypoparathyroidism?

1. Increased serum phosphate

2. Increased serum calcium

3. Decreased serum magnesium

4. Decreased serum chloride

The correct answer is: Increased serum phosphate

In patients with hypoparathyroidism, a characteristic laboratory finding is increased serum phosphate levels. The parathyroid hormone (PTH) normally regulates calcium and phosphate levels in the body; it promotes calcium reabsorption in the kidneys and stimulates the release of calcium from the bones while promoting phosphaturia, which is the excretion of phosphate in the urine. When there is insufficient PTH, as is the case in hypoparathyroidism, this regulatory mechanism is disrupted. The lack of PTH leads to diminished renal excretion of phosphate, resulting in elevated serum phosphate levels. This imbalance can cause various metabolic issues, particularly affecting calcium levels, which typically can remain low or normal despite the high phosphate. In this context, elevated serum phosphate is a hallmark finding that helps distinguish hypoparathyroidism from other conditions affecting calcium and phosphate metabolism. Recognizing this laboratory finding is crucial for diagnosing and managing the implications of hypoparathyroidism effectively.