A patient is admitted to the hospital with a diagnosis of primary hyperparathyroidism. A nurse checking the patient’s lab results would expect which of the following changes in laboratory findings?
A. Elevated serum calcium
B. Low serum parathyroid hormone (PTH)
C. Elevated serum vitamin D
D. Low urine calcium
Correct Answer: A. Elevated serum calcium
The parathyroid glands regulate the calcium level in the blood. In hyperparathyroidism, the serum calcium level will be elevated. The chronic excessive resorption of calcium from bone caused by excessive parathyroid hormone can result in osteopenia.
Option B: Parathyroid hormone levels may be high or normal but not low. The main effects of parathyroid hormone are to increase the concentration of plasma calcium by increasing the release of calcium and phosphate from bone matrix, increasing calcium reabsorption by the kidney, and increasing renal production of 1,25-dihydroxyvitamin D-3 (calcitriol), which increases intestinal absorption of calcium.
Option C: The body will lower the level of vitamin D in an attempt to lower calcium. Vitamin D levels should be measured in the evaluation of primary hyperparathyroidism. Vitamin D deficiency (a 25-hydroxyvitamin D level of less than 20 ng per milliliter) can cause secondary hyperparathyroidism, and repletion of vitamin D deficiency can help to reduce parathyroid hormone levels.
Option D: Urine calcium may be elevated, with calcium spilling over from elevated serum levels. This may cause renal stones. In addition, the chronically increased excretion of calcium in the urine can predispose to the formation of renal stones.