What is a key laboratory finding in primary hyperparathyroidism?

In primary hyperparathyroidism, a key laboratory finding is elevated serum calcium levels. This condition is characterized by excessive secretion of parathyroid hormone (PTH), which regulates calcium metabolism in the body. When PTH levels are high, they lead to increased calcium resorption from bones, enhanced intestinal absorption of calcium (through activated vitamin D), and decreased renal excretion of calcium. Consequently, these processes elevate serum calcium levels.

Elevated serum calcium is important clinically as it can lead to symptoms collectively termed "stones, bones, groans, and psychiatric overtones" due to its effects on the kidneys, bones, gastrointestinal system, and mental health. Monitoring serum calcium levels helps validate the diagnosis and guide the management of primary hyperparathyroidism.