Parathyroid Hormone
Hyperparathyroidism may be diagnosed clinically by recognising a combination of signs and symptoms – these features indicate that tests are needed which show that blood levels of calcium and parathyroid hormone are too high. As the symptoms are so vague and patients can have any combination of symptoms, they are not often no diagnosed as having a parathyroid disorder and go untreated. Other diseases can cause high blood calcium levels, but only in hyperparathyroidism is the elevated calcium the result of too much parathyroid hormone.
A blood test that accurately measures the amount of parathyroid hormone has simplified the diagnosis of hyperparathyroidism. Once the diagnosis is established, other tests may be done to assess complications – because high PTH levels can cause bones to weaken from calcium loss, a measurement of bone density can help assess bone loss and the risk of fractures.
Parathyroid Tests
Under normal conditions, a normal calcium level will be associated with a normal parathyroid hormone level. Also under normal conditions, a low serum calcium level will be associated with a high parathyroid hormone level; a high calcium level will be associated with a low parathyroid hormone level. These are all appropriate ways in which a parathyroid gland will react to calcium that is circulating in the blood as they attempt to regulate calcium in the narrow normal range.
Hyperparathyroidism is diagnosed when the parathyroid glands produce an inappropriately large amount of parathyroid hormone in the face of an elevated serum calcium.
This is straightforward and simple to measure. Another way to confirm hyperparathyroidism is by measuring the amount of calcium in the urine over a 24-hour period. If the kidneys are functioning normally, they will filter much of this calcium in an attempt to rid the body of calcium, leading to an abnormally large amount of calcium in the urine. Measuring calcium in the urine, however, is an indirect measure of parathyroid activity and is only accurate about 25% to 40% of the time.
The most accurate and definitive way to diagnose primary hyperparathyroidism is by confirming an inappropriately elevated parathyroid hormone level together with an elevated or normal serum calcium.
Parathyroid Scan
CT, Ultrasound and parathyroid scanning
A sestamibi scan is the preferred test used to find the location of the abnormal parathyroid gland. Other tests including ultrasound or CT scaning can be performed and when these tests are combined with sestamibi, they improve the chances of finding the parathyroid adenoma. The results of neck ultrasound and parathyroid scanning may be combined to increase the accuracy of finding the parathyroid adenoma. Parathyroid scanning and parathyroid imaging studies (Sestamibi, Ultrasound, or CT Scan) help find the location of the abnormally enlarged gland which is important in planning parathyroid surgery. Imaging studies are not used to make the diagnosis, only for localization – which may help localise the parathyroid adenoma during parathyroid surgery.
If you have any questions about diagnosis for hyperparathyroidism or parathyroid surgery, contact your local doctor, who will arrange for you to see a parathyroid and thyroid surgeon.
