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Parathyroid glands are located in the neck just behind the thyroid gland, hence the name parathyroid glands. In most people, there are a total of four parathyroid glands, but some may have three while others may have five.

The function of the parathyroid glands is to regulate calcium and phosphorus metabolism in the body.

   Disorders of Parathyroid Glands:

1. Primary hyperparathyroidism (overactive parathyroid glands) 

2. Secondary hyperparathyroidism (overactive parathyroid glands) 

3. Tertiary hyperparathyroidism (overactive parathyroid glands) 

4. Hypoparathyroidism (underactive parathyroid glands) 

Primary Hyperparathyroidism 

Primary hyperparathyroidism is a common disease.  Most cases of primary hyperparathyroidism are discovered incidentally when a high calcium level is found on a routine chemistry panel ordered for some other reason.  

The next step is to measure blood ionized calcium level, phosphorus level and parathyroid hormone level.  

In these patients, ionized calcium level is high, phosphorus level is low to low normal and parathyroid hormone (intact molecule) is elevated.  

Most physicians consider this set of lab testing to be diagnostic for primary hyperparathyroidism. Until a few years ago, I was one of them, but not any longer.  

In the last few years I started checking vitamin D level in most of my patients. I was amazed how prevalent vitamin D deficiency is, even in southern California. 

Vitamin D deficiency leads to secondary hyperparathyroidism, which over a period of time can lead to tertiary hyperparathyroidism (discussed below). 

In patients with tertiary hyperparathyroidism, blood ionized calcium level is high, phosphorus level is low to low normal and parathyroid hormone (intact molecule) is elevated. It is the same set of lab results considered by most physicians to be diagnostic for primary hyperparathyroidism.  

I have several cases which were diagnosed by other physicians as primary hyperparathyroidism, but actually turned out to be a combination of secondary and tertiary hyperparathyroidism due to chronic vitamin D deficiency.  

In most patients, primary hyperparathyroidism results from enlargement of one of the four parathyroid glands. This enlarged parathyroid gland produces large amounts of parathyroid hormone which in turn is responsible for the high level of calcium in the blood.  

Occasionally, primary hyperparathyroidism occurs in a familial pattern and is sometimes associated with other endocrine disorders such as pheochromocytoma. These families should be thoroughly evaluated by an endocrinologist.    

Complications of Primary Hyperparathyroidism:  

1. Kidney stones 

2. Osteoporosis 

3. Bone pains  

4. Bone fractures 

5. Rarely, a marked elevation in  blood calcium level which can cause confusion, drowsiness and even coma.    

Treatment of Primary Hyperparathyroidism:  

The patient should be thoroughly evaluated by an endocrinologist.  

Sporadic cases (as compared to familial cases) can be treated surgically or managed  conservatively under the supervision of an endocrinologist.  

Surgery should be considered if: 

A. The blood calcium level is significantly elevated.  

B. Kidney stones develop.  

C. Bone density decreases despite adequate treatment.

Familial cases are treated surgically only after they have been evaluated by an endocrinologist for other endocrine disorders especially pheochromocytoma. Undiagnosed  pheochromocytoma can cause serious complications and even death during surgery.    

A close monitoring of blood calcium and phosphorus level is important.  

Secondary Hyperparathyroidism  

Secondary hyperparathyroidism is the most common parathyroid disorder. It results from Vitamin D deficiency, which is prevalent even in sunny southern California with a very mild winter. You can imagine how prevalent it must be in places with harsh long winters such as Canada, the Northeastern U.S. and Northern Europe. 

In response to Vitamin D deficiency, the parathyroid glands produce more and more parathyroid hormone. This results in secondary hyperparathyroidism.  

The blood test in these patients shows a normal calcium level, a normal phosphorus level and an elevated parathyroid hormone (intact molecule) level.  

Just looking at the elevated parathyroid hormone level, some physicians jump to the conclusion that it is primary hyperparathyroidism and send these patients for surgery.   

I have seen these kind of unfortunate mismanaged cases.  

Obtaining a Vitamin D level is crucial in these patients in order to reach the correct diagnosis.  

Also it is important to do the correct test for Vitamin D.   

There are two tests for vitamin D level: 25 OH Vitamin D and 1,25 OH Vitamin D. 25 OH Vitamin D (and NOT the 1,25 OH  Vitamin D) is the correct test for diagnosing Vitamin D deficiency.  

In patients with secondary hyperparathyroidism, 25 OH vitamin D is low. However, 1,25 OH vitamin D is normal or may even be high.  

Another common problem is the normal range printed on the lab form. In my experience, most normal ranges printed on the lab forms are incorrect. A 25 OH vitamin D level less than 30 ng/ml is considered low by most endocrinologists.

In patients with chronic kidney failure (often patients on dialysis), a special form of vitamin D deficiency takes place. In these patients, 1,25 OH vitamin D level is also low, as the kidneys cannot convert 25 OH vitamin D into 1,25 OH vitamin D.  

Complications of Secondary Hyperparathyroidism 

1. Bone pains

2. Muscle pains

3. Osteoporosis

4. Bone fractures

 Treatment of Secondary Hyperparathyroidism  

Treatment of secondary hyperparathyroidism is with high doses of Vitamin D.

Close monitoring of blood calcium and phosphorus level is important.     

Tertiary Hyperparathyroidism  

If secondary hyperparathyroidism remains untreated, it leads to tertiary hyperparathyroidism.

In this case, one or more of the parathyroid glands gets enlarged and keeps producing large amounts of parathyroid hormone even if the blood level of calcium gets elevated.  

Now a patient's blood level of calcium is also elevated in addition to all the lab tests mentioned above in secondary hyperparathyroidism.

Tertiary hyperparathyroidism is a more severe form of secondary hyperparathyroidism.  

Complications of Tertiary Hyperparathyroidism  

1. Kidney stones.  

2. Osteoporosis.  

3. Bone pains.  

4. Bone fractures.  

5. Rarely, a marked elevation in  blood calcium level can cause confusion, drowsiness and even coma.    

Treatment of Tertiary Hyperparathyroidism:  

In addition to Vitamin D supplementation, patients may need surgery if:

A. The blood calcium level is significantly elevated.

B. Kidney stones develop.

C. Bone density decreases despite adequate treatment.

Close monitoring of blood calcium and phosphorus level is important.  


The most common cause for hypoparathyroidism is surgical removal of the parathyroid glands at the time of thyroid surgery.

Rarely, it can be congenital or acquired as an autoimmune disorder.

Hypoparathyroidism results in a low level of blood calcium and a high level of blood phosphorus. 

Symptoms of Hypoparathyroidism

Symptoms are due to the low calcium level and include muscle spasms and twitching.

A severely low calcium level can cause cardiac arrest.  

Treatment of Hypoparathyroidism

Treatment of a patient with hypoparathyroidism is with calcium and vitamin D supplementation in high doses.  

Close monitoring of calcium and phosphorus is important.  



This article was written by Sarfraz Zaidi, MD, FACE. Dr. Zaidi specializes in Diabetes, Endocrinology and Metabolism.

Dr. Zaidi is a former assistant Clinical Professor of Medicine at UCLA and Director of the Jamila Diabetes and Endocrine Medical Center in Thousand Oaks, California.

For details on secondary and tertiary hyperparathryoidism, please refer to Dr. Zaidi's book, "Power of Vitamin D."  

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