Parathyroid Hormone (PTH) Test
What Is a Parathyroid Hormone (PTH) Test?
The four-sectioned parathyroid glands are located in your neck, at the edge of the thyroid gland. They’re responsible for regulating calcium, vitamin D, and phosphorus levels in the blood and bones.
The parathyroid glands release a hormone called parathyroid hormone (PTH), also known as parathormone. PTH helps regulate calcium levels in the blood.
Calcium imbalances in the blood may be a sign of parathyroid gland or PTH issues. Calcium levels in the blood signal the parathyroid glands to release PTH. When calcium levels are low, the parathyroid glands increase PTH production. When calcium levels are high, the glands slow down the secretion of PTH.
Some symptoms and medical conditions may cause your doctor to measure how much PTH is in your blood. Because of the relationship between calcium and PTH in the blood, both are often tested at the same time.
Why Do I Need a Parathyroid Hormone Test?
Healthy calcium levels are essential for your body to function properly. Your doctor may need to measure PTH if:
- you’re having symptoms of too much calcium in the blood (fatigue, nausea, thirst, abdominal pain)
- you’re having symptoms of too little calcium in the blood (abdominal pain, muscle cramps, tingling fingers)
- your blood calcium test comes back abnormal
- they need to figure out the cause of too much or too little calcium in the blood
Too much calcium could be a sign of hyperparathyroidism. This is a condition caused by overactive parathyroid glands that produce too much PTH. Excess calcium in the blood can lead to kidney stones, irregular heartbeats, and brain abnormalities.
Too little calcium could be a sign of hypoparathyroidism. This is a condition caused by underactive parathyroid glands that aren’t producing enough PTH. Not enough calcium in the blood could lead to:
- osteomalacia (weakened bones)
- muscle spasms
- heart rhythm disturbances
- tetany (overstimulated nerves)
Your doctor may also order this test to:
- check parathyroid functioning
- distinguish between parathyroid-related and nonparathyroid-related disorders
- monitor the effectiveness of treatment in parathyroid-related issues
- determine the cause of low phosphorus levels in the blood
- determine why severe osteoporosis isn’t responding to treatment
- monitor chronic conditions, such as kidney disease
What Is the Procedure for a Parathyroid Hormone Test?
You’ll need to get your blood drawn for a PTH test. Your doctor will recommend a PTH test:
- if you have signs of too much or too little calcium in your blood
- before having hyperparathyroidism surgery
- to assess the functioning of your parathyroid gland.
Before the Test
You may need to refrain from eating or drinking for a specific period of time before the blood test. Ask your doctor about specific pretest requirements. Before having this test, tell your doctor if you have hemophilia, a history of fainting, or any other condition.
The process of taking a blood sample for testing is called venipuncture. They usually draw blood from a vein from the inner elbow or back of the hand.
Your doctor or a lab technician will sterilize the area with an antiseptic. Then they’ll wrap a plastic band around your arm to apply pressure and to help your veins swell with blood. After the veins swell, they’ll insert a sterile needle directly into the vein. The blood will collect in an attached vial. When there’s enough blood for the sample, they’ll untie the plastic band and remove the needle from the vein. They’ll clean and bandage the site of the needle insertion if necessary.
Some people experience only slight pain from the needle prick, while others may feel moderate pain, especially if the vein is difficult to locate. It’s common for the spot to throb after the procedure. Some bleeding is also common, as the needle will break the skin. For most people, bleeding is slight and won’t cause any issues.
Infants and Young Children
The testing process may be different for infants and young children. The doctor or lab technician may make a small cut to allow blood to come to the surface. They’ll then use a test strip or slide to collect a small sample of blood. They’ll clean and bandage the area if necessary.
What Do the Test Results Mean?
Your doctor will evaluate your PTH and calcium test results together to assess whether your levels are within normal ranges. If PTH and calcium are in balance, your parathyroid glands are very likely functioning properly.
If PTH levels are low, you may have a condition causing low calcium levels. Or, you may have an issue with your parathyroid glands that’s causing hypoparathyroidism.
If PTH levels are high, you could have hyperparathyroidism. Hyperparathyroidism is commonly due to a benign parathyroid tumor. If PTH levels are normal and calcium levels are low or high, the issue may not be your parathyroid glands.
High PTH levels could indicate:
- conditions that cause increased phosphorus levels, like chronic kidney disease
- the body isn’t responding to PTH (pseudohypoparathyroidism)
- swelling or tumors in the parathyroid glands
- pregnancy or breastfeeding in a woman (uncommon)
High PTH levels could also indicate a lack of calcium. This could mean you’re not getting enough calcium in your diet. It can also mean that your body isn’t absorbing calcium, or you’re losing calcium through urination.
High PTH levels also point to vitamin D disorders. Maybe you’re not getting enough sunlight, or your body has trouble breaking down, absorbing, or using this vitamin. Vitamin D deficiency can lead to muscle and bone weakness.
Low PTH levels could indicate:
- an autoimmune disorder
- cancer originating from another part of the body has spread to the bones
- you’ve ingested excess calcium over a long period of time (from milk or certain antacids)
- low levels of magnesium in the blood
- radiation exposure to the parathyroid glands
- vitamin D intoxication
- sarcoidosis (a disease causing inflammation to tissues)
If either PTH or calcium levels are too high or too low, your doctor may want to do additional testing to more clearly identify the problem.