THE thyroid gland is a well-known bodily organ, with a general awareness that an underactive thyroid is linked to weight gain, but a thyroid gland producing too much thyroid hormone can cause weight loss.

Thyroid function tests are among the most common blood tests requested in general practice. Yet the parathyroid glands, and the conditions associated with their dysfunction, are perhaps less well known.

The parathyroid glands are four pea-sized structures, sitting on the back of the thyroid. The parathyroid glands produce parathyroid hormone, often abbreviated to PTH. PTH controls the amount of calcium in the blood, through a system known as negative feedback. When levels of calcium are adequate the parathyroid glands produce less PTH, when calcium levels are low, more PTH is secreted.

Hyperparathyroidism has three main causes. A single benign parathyroid tumour, known as an adenoma, is the commonest. One or more parathyroid glands may enlarge, secreting excess PTH. This is referred to as hyperplasia. Thankfully, a malignant parathyroid tumour, producing too much of the hormone is rare.

Persons with excess calcium in the blood may be completely well. Complaints are often quite vague and varied, with aches and pains, increased sleeping and mood changes commonly reported. Untreated, too much calcium, referred to as hypercalcaemia, increases the risk of osteoporosis, kidney stones, raised blood pressure and heart disease. Life threateningly high calcium levels will cause nausea, vomiting and confusion. This is a medical emergency.

Hypoparathyroidism may result from damage to the glands, for example after neck surgery or radiotherapy to the area. They may be destroyed by an autoimmune condition, where the body mistakenly attacks its own tissue. More rarely, persons are born without parathyroid glands, for example in Di George Syndrome.

Low PTH results in low calcium. Sufferers may experience muscle cramps and spasms, tingling in the lips, fingers and toes, as well as memory issues. As with hyperparathyroidism, symptoms are often varied and indeed multiple, and might not immediately suggest hypoparathyroidism as the most likely cause.

PTH blood tests are usually requested as a second line investigation if calcium levels, also called a bone profile, are found to be abnormal.

A parathyroid scan uses the safe radioactive substance sestamibi, (MIBI for short), injected into the body. An overactive parathyroid gland(s) will light up as a hot-spot. For those with borderline raised calcium levels, a watch and wait approach may be adopted, but definitive treatment is surgery to remove the affected gland. This can often be done through a very small incision in the neck.

Hypoparathyroidism, resulting in low levels of calcium, requires lifelong supplementation, with regular blood tests to check levels are adequate. A good dietary intake of calcium rich foods may also help maintain adequate levels.