From the Guidelines
Low parathyroid hormone (PTH) with normal calcium levels is most commonly caused by adynamic bone disease, which is associated with oversuppression of PTH, often due to aggressive vitamin D treatment, chronic positive calcium balance, or following parathyroidectomy, as well as conditions like aging and diabetes. This condition can lead to low-turnover bone disease, which has been increasingly recognized in patients with chronic kidney disease (CKD) 1. The use of high-dose calcium salts for phosphate binding and more frequent and aggressive vitamin D treatment can contribute to the development of adynamic bone lesions 1.
Some key factors to consider in the evaluation of low PTH with normal calcium levels include:
- Oversuppression of PTH due to vitamin D treatment or other factors
- Chronic positive calcium balance
- Parathyroidectomy
- Aging and diabetes, which can predispose to osteoporosis
- Use of certain medications, such as thiazide diuretics, which can reduce calcium excretion while suppressing PTH
- Familial hypocalciuric hypercalcemia (FHH), a genetic mutation affecting calcium-sensing receptors
- Malignancies producing PTH-related protein (PTHrP), which can mimic PTH effects while suppressing actual PTH production
- Recovery from hypoparathyroidism, which may show temporarily low PTH with normalizing calcium levels
- Laboratory errors or sample handling issues, which can also produce these findings 1.
When evaluating a patient with low PTH and normal calcium levels, it is essential to review their medication history, check vitamin D levels, assess family history for calcium disorders, and consider malignancy screening if clinically indicated 1.
From the Research
Causes of Low PTH and Normal Calcium
- Low parathyroid hormone (PTH) levels can be caused by various factors, including damage to the parathyroid glands during thyroid surgery 2, 3.
- Hypoparathyroidism, a disorder characterized by low serum calcium and elevated serum phosphate levels, is often caused by the inadvertent damage to the parathyroid glands during thyroid surgery 2.
- Autoimmune destruction of the parathyroid glands and other genetic causes can also lead to low PTH levels 3.
- In some cases, low PTH levels can be caused by vitamin D unresponsiveness, which can lead to uncontrolled hypocalcemia 4.
- Normal calcium levels can be maintained in patients with low PTH levels through treatment with oral calcium and active vitamin D supplementation 2, 5, 3.
- However, high doses of calcium and vitamin D may be required, which can add to the risk of long-term soft tissue calcifications 3.
- Replacement therapy with recombinant human PTH(1-84) has been shown to be effective in maintaining normal calcium levels and reducing the risk of soft tissue calcifications 2, 3.
Treatment Options
- Treatment options for low PTH and normal calcium levels include oral calcium and active vitamin D supplementation 2, 5, 3.
- Replacement therapy with recombinant human PTH(1-84) is also available 2, 3.
- Teriparatide, a recombinant human PTH(1-34), has been shown to be effective in treating hypoparathyroidism 4, 5.
- Multipulse subcutaneous infusion of teriparatide has been shown to be an effective and safe alternative for patients with vitamin D unresponsiveness 4.