Hyperparathyroidism is a hormonal disorder caused by the parathyroid glands in the neck producing too much parathyroid hormone (PTH).
The condition can be diagnosed based on the results of blood tests, X-rays and computed tomography (CT) or ultrasound scans. The gold standard for diagnosis is the parathyroid immunoassay, which is used to determine the patient’s PTH level.
Once an increased PTH level is detected, the type of hyperparathyroidism a patient has needs to be determined. There are two main types of hyperparathyroidism, primary and secondary. In primary hyperparathyroidism, as the blood parathyroid hormone level begins to rise, the blood calcium level also rises. Renal tubular phosphate reabsorption is also often decreased (in around 50% of cases), leading to a low blood phosphate level. Blood tests may therefore indicate hypercalcemia and hypophosphatemia.
Secondary hyperparathyroidism is caused by another underlying condition such as kidney failure or vitamin D deficiency causing a low blood calcium level. The parathyroid gland compensates by producing excess PTH to try and restore the calcium level. Renal disease may also lead to an elevated phosphate level. Blood tests will therefore show a raised PTH in the presence of a low blood calcium level and perhaps a raised blood phosphate level.
In cases where secondary hyperparathyroidism is left untreated, the parathyroid glands remain in a permanently overactive state, which is referred to as tertiary hyperparathyroidism. This condition is often seen in chronic kidney failure patients.
Other tests that may be conducted include the following:
- Detailed kidney function tests to rule out renal failure or renal stones as the cause of parathyroid overactivity
- Blood test for 25-hydroxy-vitamin D blood to detect vitamin D deficiency
- X-rays and CT scans to assess bone damage
- A 24-hour urine test to check urinary calcium, creatinine and phosphate levels
Reviewed by Sally Robertson, BSc