What Are the Parathyroid Glands? Understanding Primary Hyperparathyroidism
Written by John P. Sabra, MD FACS
Updated May 2026
Educational only. This article is not medical advice. Always consult your physician about your individual situation.
Most patients have never heard of the parathyroid glands before a doctor tells them something is wrong with one. They are not the thyroid. They are four tiny structures, each about the size of a grain of rice, that sit behind the thyroid gland in the neck and perform one of the most essential jobs in the body: keeping calcium in balance.
When one of those glands grows into a small benign tumor called an adenoma and produces too much parathyroid hormone, the result is a condition called primary hyperparathyroidism. It is one of the most common endocrine disorders in adults, affecting roughly 1 in 200 to 1 in 1,000 people. It is three times more common in women than men. And it is one of the most frequently missed, misattributed, and under-treated diagnoses in medicine.
What the Parathyroid Glands Actually Do
Most people have four parathyroid glands, two on each side, sitting immediately behind the thyroid. Each is approximately 3 to 5 millimeters in size and weighs less than 100 milligrams. Despite their small size, they perform a task the body cannot live without: regulating your calcium.
Calcium is not just a building block of bones. It governs how nerves fire, how muscles contract, how the heart beats, and how hundreds of cellular processes function. The body maintains blood calcium within an extremely narrow range, and the parathyroid glands are the primary instrument of that regulation. They do it by producing parathyroid hormone (PTH), which raises calcium when it falls too low, by pulling it from bones, increasing absorption from food in the intestines, and reducing calcium loss through the kidneys.
When calcium rises, the parathyroid glands sense it and turn down PTH production. When calcium falls, they turn it back up. It is a constant, automatic feedback loop, a biological thermostat that operates continuously throughout your life.
What Happens When a Parathyroid Gland Goes Wrong
In primary hyperparathyroidism, one or more parathyroid glands develops a partial or complete failure of that feedback mechanism. The gland keeps producing PTH even when calcium is already elevated, as if the thermostat is stuck. The result is chronically elevated PTH and chronically elevated calcium, with consequences that ripple through bones, kidneys, the brain, the digestive system, and the heart.
In roughly 85% of cases, the cause is a single benign adenoma, one overactive gland that needs to be removed. In about 10 to 15% of cases, multiple glands are affected, a condition called hyperplasia. Parathyroid cancer is extremely rare, accounting for less than 1% of all cases.
The parathyroid glands are entirely separate from the thyroid gland — they just happen to live in the same neighborhood. Having a parathyroid problem does not mean you have a thyroid problem, and vice versa. However, because they are anatomically adjacent, surgery for one condition requires careful attention to protect the other. A surgeon operating on parathyroid disease needs to be as skilled at protecting the thyroid and its nerves as a surgeon operating on the thyroid itself.
Why Primary Hyperparathyroidism Is So Often Missed
Primary hyperparathyroidism was once discovered when patients arrived with kidney stones, fractures, or severe bone pain. Since the widespread adoption of standard blood panels in the 1970s, the disease is now most commonly found as an incidental elevated calcium on a routine lab panel, often years before the patient has developed any obvious complication.
The problem is that an elevated calcium on a routine lab is frequently dismissed, repeated, and then filed away without investigation. The symptoms that accompany it, fatigue, brain fog, poor sleep, mild depression, body aches, are attributed to aging, stress, thyroid problems, menopause, or anxiety. Patients spend years feeling unwell without anyone connecting their symptoms to a calcium number that was slightly high on a lab report from three years ago.
If your calcium has been elevated on more than one blood test, it warrants investigation, not a repeat in six months and a wait. The appropriate next step is a PTH level drawn at the same time as the calcium. If both are elevated, or if PTH is inappropriately normal in the presence of high calcium, the diagnosis of primary hyperparathyroidism is very likely and a referral to a specialist is appropriate.
The diagnosis of primary hyperparathyroidism is biochemical — it is made by blood tests, not imaging. Elevated calcium combined with an elevated or inappropriately normal PTH is the diagnostic finding. Imaging (ultrasound, sestamibi scan) comes later, to help plan potential surgery. A patient who has been told their calcium is high but has not had a PTH level checked has not been fully evaluated.
Primary vs. Secondary vs. Tertiary Hyperparathyroidism
Not all high PTH levels mean the same thing. Primary hyperparathyroidism is caused by a problem within the parathyroid gland itself, an adenoma or hyperplasia that produces PTH regardless of calcium levels. Secondary hyperparathyroidism is a normal response to chronically low calcium, most commonly from vitamin D deficiency or chronic kidney disease, the glands are doing their job correctly, but the underlying condition keeps driving calcium down. Tertiary hyperparathyroidism occurs when chronically stimulated parathyroid glands in secondary disease develop autonomous function, as sometimes seen in long-standing kidney failure.
The distinction matters because the treatment is entirely different. Secondary hyperparathyroidism from vitamin D deficiency is treated with vitamin D supplementation, not surgery. This is one reason why vitamin D status should always be assessed when hyperparathyroidism is being evaluated.
The Bottom Line
The parathyroid glands are small, largely unknown to most patients, and responsible for a disease that affects millions of adults, many of whom are walking around feeling chronically unwell without knowing why. Primary hyperparathyroidism is not rare, and it is not benign if left untreated over time. It is a curable disease, and the cure is surgical.
If your calcium is elevated and no one has checked your PTH, ask for it at your next appointment. That single test may explain years of symptoms.
References
- Wilhelm SM, et al. AAES Guidelines for the Definitive Management of Primary Hyperparathyroidism. JAMA Surg. 2016.
- NIH NIDDK — Primary Hyperparathyroidism: Patient Information.
- American Association of Endocrine Surgeons — Patient Resources.
This article was written byJohn P. Sabra, MD FACS and is intended for patient education only. It does not constitute medical advice and does not replace a consultation with your physician. Individual patient circumstances and clinical judgment determine the appropriate evaluation and management for every patient.
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