Parathyroid Hormone (PTH)

What it is

Parathyroid hormone, often shortened to PTH, is a vital hormone produced by tiny glands in your neck called the parathyroid glands. There are usually four of these glands, each about the size of a grain of rice, located behind your thyroid gland.

PTH plays a crucial role in maintaining the right balance of calcium in your blood. Calcium is essential for many bodily functions, including nerve signalling, muscle contraction, and keeping your bones strong. PTH works like a thermostat for your calcium levels, constantly monitoring and adjusting them.

When your blood calcium levels start to drop too low, your parathyroid glands release more PTH. This hormone then acts on your bones, kidneys, and intestines to bring your calcium levels back up.

Why it matters

The level of PTH in your blood is a key indicator of how well your parathyroid glands are working and how your body is managing calcium. Maintaining a stable calcium level is critical for overall health.

If PTH levels are too high or too low, it can signal that there's an imbalance in your calcium metabolism, which can affect your bones, kidneys, and other parts of your body. For instance, persistently high PTH can lead to calcium being leached from your bones, making them weaker over time. Conversely, very low PTH can mean your body isn't getting enough calcium, which is also problematic.

The typical reference range for PTH in the UK is between 1.6 and 6.9 pmol/l, though this can vary slightly between laboratories. Your doctor will interpret your result in the context of your overall health and other test results.

What can cause it to be high or low

Several factors can influence your PTH levels.

High PTH levels are often seen when your body is trying to compensate for low calcium. This can happen due to:

• Vitamin D deficiency: Vitamin D is essential for absorbing calcium from your diet. If you don't have enough vitamin D, your calcium levels can drop, prompting your parathyroid glands to produce more PTH.
• Chronic kidney disease (CKD): Damaged kidneys struggle to activate vitamin D and excrete phosphate, both of which can lead to low calcium and high PTH.
• Certain types of tumours: In rare cases, tumours in the parathyroid glands themselves (parathyroid adenomas) can lead to overproduction of PTH, a condition called primary hyperparathyroidism.
• Malabsorption issues: Conditions affecting your gut's ability to absorb nutrients, including calcium and vitamin D, can also lead to higher PTH.
• Low calcium intake: Not consuming enough calcium in your diet over a prolonged period can trigger an increase in PTH.

Low PTH levels are usually associated with high calcium levels in the blood. This can be due to:

• Overactive parathyroid glands (rare): Sometimes, the parathyroid glands produce too much PTH, leading to high calcium levels. The body then tries to correct this by suppressing PTH production, but in some cases, the glands themselves are the source of the problem.
• Certain autoimmune conditions: In some instances, the body's immune system may mistakenly attack the parathyroid glands.
• Low magnesium levels: Severe magnesium deficiency can sometimes impair PTH secretion.
• Certain medications: Some drugs can affect PTH levels.

Lifestyle factors that may help

Certain lifestyle choices can support healthy calcium and bone metabolism, which in turn can influence PTH levels. These are areas you might wish to discuss with your GP:

• Dietary calcium intake: Ensuring your diet includes sufficient calcium-rich foods, such as dairy products, leafy green vegetables, and fortified foods, is important.
• Vitamin D levels: Getting adequate vitamin D is crucial. This can come from sensible sun exposure (though this varies depending on skin type and time of year), as well as from certain foods like oily fish and fortified products.
• Regular physical activity: Weight-bearing exercises, such as walking, jogging, or strength training, can help maintain bone density and support overall bone health.
• Limiting alcohol and avoiding smoking: Excessive alcohol consumption and smoking can negatively impact bone health and calcium balance.

Questions to discuss with your GP

If you have had a PTH test or are concerned about your calcium or bone health, here are some questions you might consider discussing with your GP:

• What does my PTH result mean in the context of my overall health?
• Are my calcium and vitamin D levels also within the normal range?
• Could my current symptoms or medical history be related to my PTH level?
• Are there any specific dietary adjustments or lifestyle changes that would be beneficial for me?
• Do I need any further tests to investigate my PTH level or bone health?
• What are the potential long-term implications of my PTH result?