North American Veterinary Licensing Examination (NAVLE) Practice Test

What would you expect to find in a chemistry panel of a dog with primary hyperparathyroidism?

1. Hypocalcemia, hyperphosphatemia

2. Hypercalcemia, hyperphosphatemia

3. Hypercalcemia, hypophosphatemia

4. Hypocalcemia, hypophosphatemia

The correct answer is: Hypercalcemia, hypophosphatemia

In a dog with primary hyperparathyroidism, the primary endocrine disturbance involves the overproduction of parathyroid hormone (PTH), typically due to a parathyroid adenoma. PTH regulates calcium and phosphate levels in the body. With primary hyperparathyroidism, the excess secretion of PTH leads to increased calcium resorption from bones, increased intestinal absorption of calcium (aided by increased vitamin D), and increased renal tubular reabsorption of calcium. As a result, hypercalcemia (elevated calcium levels) is the hallmark finding in laboratory tests. Alongside the hypercalcemia, the effect of increased PTH is often a decrease in phosphorus levels due to PTH's action to promote phosphate excretion by the kidneys. Therefore, you would expect to find hypercalcemia and hypophosphatemia in the chemistry panel of a dog with this condition. The other answer choices suggest combinations that do not align with the physiological effects of elevated PTH levels. Hypocalcemia would indicate a low level of calcium, which is not consistent with primary hyperparathyroidism. Hyperphosphatemia suggests elevated phosphate levels, which also contradicts the typical findings since PTH tends to lower phosphate due to increased urinary excretion.