Parathyroid hormone (PTH) is a chemical messenger produced by the parathyroid glands, which are four small glands located in the neck, typically behind the thyroid gland. This hormone plays a role in maintaining the body’s balance of certain minerals.
The Role of PTH and its Normal Range
Parathyroid hormone has a primary function: regulating calcium and phosphate levels in the blood. When blood calcium levels fall, the parathyroid glands release PTH, which then stimulates the release of calcium from the bones into the bloodstream.
PTH also acts on the kidneys, reducing the loss of calcium in urine and promoting the production of active vitamin D. This active vitamin D, in turn, indirectly increases calcium absorption from food in the intestine. The normal reference range for intact PTH typically falls between 10 to 55 picograms per milliliter (pg/mL), though slight variations can occur between laboratories. Maintaining PTH levels within this range is important for proper nerve and muscle function, as well as for strong bones.
Understanding Elevated PTH Levels
Higher-than-normal PTH levels, known as hyperparathyroidism, can arise from various causes. Primary hyperparathyroidism occurs when one or more of the parathyroid glands become overactive, often due to a noncancerous growth called an adenoma, or enlargement of the glands. This leads to an overproduction of PTH and elevated calcium levels in the blood. Sustained high calcium levels can lead to symptoms like fatigue, bone pain, and kidney stones.
Secondary hyperparathyroidism results from another underlying condition that causes low blood calcium. Chronic kidney disease is a common cause, as impaired kidney function prevents the activation of vitamin D, leading to reduced calcium absorption. The parathyroid glands then compensate by producing more PTH to raise calcium levels. Severe vitamin D deficiency or insufficient calcium intake can also trigger this increase in PTH.
Understanding Low PTH Levels
Lower-than-normal PTH levels, called hypoparathyroidism, means the parathyroid glands are not producing enough of the hormone. The most frequent cause is accidental damage to the parathyroid glands during neck or thyroid surgery, which accounts for about 75% of cases. This damage can occur immediately after surgery or years later.
Autoimmune conditions can also lead to hypoparathyroidism, where the body’s immune system damages the parathyroid glands. Genetic factors can also play a role, with some individuals born with malfunctioning, malformed, or missing parathyroid glands. Low PTH levels result in low blood calcium (hypocalcemia) and high blood phosphate levels, which can cause symptoms such as tingling in the hands or around the mouth and muscle cramps.
Interpreting Results and When to Seek Medical Advice
Interpreting PTH test results requires careful consideration by a healthcare professional. An abnormal PTH level often prompts further diagnostic tests to determine the underlying cause. These additional tests may include checking calcium, vitamin D, phosphate, and kidney function. For instance, if PTH is high but calcium is low, it suggests the parathyroid glands are attempting to raise calcium, indicating a problem outside the glands.
Conversely, if calcium is high but PTH is in the normal range, it may still be considered “inappropriate” because PTH should be suppressed by high calcium. Your doctor will consider these results alongside your symptoms, medical history, and family history to provide a personalized diagnosis and discuss appropriate treatment options. Consult a healthcare provider for any concerns about PTH levels, as they can guide your care.