Hyperparathyroidism occurs when the parathyroid glands produce excess parathyroid hormone (PTH), leading to high blood calcium. These small glands, typically four, are located in the neck, near the thyroid. Early detection is important for managing the condition and preventing complications.
Understanding Hyperparathyroidism
The parathyroid glands regulate calcium and phosphate balance. They secrete parathyroid hormone (PTH), which acts on bones, kidneys, and the small intestine. When overactive, they produce too much PTH, releasing calcium from bones into the bloodstream and increasing kidney reabsorption.
Hypercalcemia (high blood calcium) affects various bodily functions. Individuals might experience non-specific symptoms such as fatigue, increased thirst, frequent urination, muscle weakness, and bone or joint pain. Kidney stones are also common. While these symptoms can be subtle and overlap with other conditions, their presence can prompt a healthcare provider to consider testing for hyperparathyroidism.
Key Blood Tests for Diagnosis
Diagnosing hyperparathyroidism primarily involves blood tests that measure key substances related to calcium metabolism. These tests are usually performed together to provide a comprehensive picture of the body’s calcium regulation.
An elevated serum calcium level is a primary indicator. Normal total serum calcium in adults typically ranges from 8.5 to 10.2 mg/dL (2.1 to 2.55 mmol/L), though laboratory ranges may vary. Persistent high calcium levels often trigger further investigation.
Measuring parathyroid hormone (PTH) levels is crucial. PTH regulates blood calcium. In healthy individuals, high calcium should lead to low PTH. However, in hyperparathyroidism, PTH levels are elevated or “inappropriately normal” despite high calcium, indicating the glands are not responding correctly.
The intact PTH test, measuring the active form, is standard. Normal intact PTH levels typically range from 10 to 65 pg/mL, but lab ranges vary.
Serum phosphate levels are also checked. PTH influences kidney phosphate excretion. In hyperparathyroidism, blood phosphate levels can be low or in the lower end of the normal range because PTH promotes its elimination through urine.
Assessing vitamin D levels is also part of the diagnostic process. Vitamin D is necessary for calcium absorption from the intestines. While deficiency can cause PTH levels to rise (secondary hyperparathyroidism), optimizing vitamin D is important for accurate diagnosis and bone health. Low vitamin D levels are common in hyperparathyroidism.
Interpreting Your Test Results
Interpreting blood test results involves looking at the relationship between calcium and PTH levels, rather than just individual values. This helps distinguish between different types of hyperparathyroidism and other conditions affecting calcium.
Primary hyperparathyroidism is diagnosed when blood tests show elevated calcium levels accompanied by elevated or “inappropriately normal” PTH levels. An “inappropriately normal” PTH means the PTH level is too high given the elevated calcium, which should normally suppress PTH production. This combination points to a problem within the parathyroid glands, often an overactive gland.
Secondary hyperparathyroidism presents a different profile. PTH levels are high as a compensatory response to persistently low calcium or vitamin D levels. Conditions like chronic kidney disease or severe vitamin D deficiency can lead to it. The parathyroid glands work harder to raise calcium, but the underlying issue is not with the glands themselves. Addressing the underlying cause, such as vitamin D supplementation, can often resolve secondary hyperparathyroidism.
Healthcare providers use established normal ranges for these tests, but also consider the patient’s overall clinical picture. A diagnosis is rarely made based on a single test result. Instead, multiple measurements and a careful assessment of symptoms are often required to confirm hyperparathyroidism.
Further Evaluation for Diagnosis
Beyond primary blood tests, additional evaluations may refine the diagnosis, assess hyperparathyroidism’s impact, or differentiate it from other conditions. These tests provide detailed insights but are not typically the first diagnostic step.
A 24-hour urine calcium collection measures calcium excreted in urine. This test differentiates primary hyperparathyroidism from familial hypocalciuric hypercalcemia (FHH), a rare genetic condition. In primary hyperparathyroidism, urinary calcium excretion is often normal or elevated. In contrast, FHH shows elevated blood calcium but unusually low calcium excretion in the urine, with a calcium-to-creatinine clearance ratio typically less than 0.01. This distinction is important because FHH is generally benign and does not require surgical treatment, unlike symptomatic primary hyperparathyroidism.
A bone density (DEXA) scan assesses the effect of chronic high PTH on bone health. Elevated PTH pulls calcium from bones, increasing the risk of bone thinning (osteopenia) and osteoporosis. While a DEXA scan does not directly diagnose hyperparathyroidism, it helps determine the severity of bone involvement, which can influence treatment decisions. It is useful for evaluating cortical bone loss, especially in areas like the forearm.