What does an abnormal Parathyroid Hormone (PTH) level, either low or high, indicate regarding elevated parathyroid hormone?

From the Guidelines

High PTH levels indicate elevated parathyroid hormone, while low PTH levels indicate hypoparathyroidism, a condition where the body produces insufficient parathyroid hormone. PTH stands for parathyroid hormone, which is produced by the parathyroid glands in the neck. Normal PTH levels typically range from 10-65 pg/mL, though reference ranges may vary slightly between laboratories. When a blood test shows high PTH levels, it indicates that the parathyroid hormone is elevated above the normal range. This elevation can occur due to conditions like primary hyperparathyroidism (often caused by a parathyroid adenoma), secondary hyperparathyroidism (commonly due to vitamin D deficiency or kidney disease), or tertiary hyperparathyroidism, as noted in a study published in the Kidney International journal 1.

Key Points to Consider

• Elevated PTH levels often lead to increased calcium levels in the blood as the hormone works to pull calcium from bones.
• The optimal PTH level in patients with CKD not on dialysis remains undefined, but high and progressively increasing PTH levels warrant investigation, according to a study published in the Kidney International journal 1.
• Increased PTH and incident secondary hyperparathyroidism are independently associated with CKD progression and cardiovascular events, mortality, and fractures, as observed in a study published in the International Journal of Surgery 1.
• Low PTH levels, on the other hand, indicate hypoparathyroidism, which is a different condition altogether where the body produces insufficient parathyroid hormone.

Clinical Implications

• The management of PTH levels is crucial in patients with chronic kidney disease (CKD), as elevated PTH levels can lead to increased morbidity and mortality, as noted in a study published in the American Journal of Kidney Diseases 1.
• The use of vitamin D metabolites, such as calcitriol, can help lower PTH levels and improve bone histology in patients with CKD, as observed in a study published in the American Journal of Kidney Diseases 1.
• However, the safety of these metabolites must be carefully monitored, and hypercalcemia must be avoided, as noted in a study published in the Kidney International journal 1.

From the FDA Drug Label

At baseline the mean (SE) serum calcium was 14.1 (0.4) mg/dL. Approximately 60% of patients with mild (iPTH ≥ 300 to ≤ 500 pg/mL), 41% with moderate (iPTH > 500 to 800 pg/mL), and 11% with severe (iPTH > 800 pg/mL) secondary HPT achieved a mean iPTH value of ≤ 250 pg/mL.

Elevated parathyroid hormone (PTH) is indicated by high iPTH levels.

• Mild secondary HPT is defined as iPTH ≥ 300 to ≤ 500 pg/mL.
• Moderate secondary HPT is defined as iPTH > 500 to 800 pg/mL.
• Severe secondary HPT is defined as iPTH > 800 pg/mL. The goal of treatment is to achieve an iPTH of ≤ 250 pg/mL 2.

From the Research

Parathyroid Hormone (PTH) Levels

• Elevated parathyroid hormone (PTH) levels can indicate primary hyperparathyroidism (PHPT) or secondary hyperparathyroidism (SHPT) 3, 4.
• PHPT is characterized by hypercalcemia with elevated or inappropriately normal PTH levels, while SHPT is caused by a physiologic stimulation to PTH secretion 4.
• Normocalcemic primary hyperparathyroidism (NPHPT) is a condition where PTH levels are elevated despite normal calcium levels, and can be difficult to distinguish from SHPT 4.

Low or High PTH Levels

• Elevated PTH levels do not necessarily mean high PTH, as immunoassay interference can result in falsely elevated readings 5.
• Low PTH levels are not typically associated with elevated parathyroid hormone, but rather with hypoparathyroidism or other conditions 6.
• Secondary hyperparathyroidism can occur in patients with primary osteoporosis and osteopenia, and may require extraordinary measures to correct, including large doses of vitamin D 6.

Diagnosis and Treatment

• Diagnosis of PHPT or SHPT requires careful evaluation of PTH levels, calcium levels, and other biochemical variables, as well as imaging studies and medical history 3, 4.
• Treatment of PHPT may involve parathyroidectomy, medical management with cinacalcet or bisphosphonates, and optimization of calcium and vitamin D intake 3, 7.
• Treatment of SHPT typically involves addressing the underlying cause of the physiologic stimulation to PTH secretion, such as vitamin D deficiency or kidney disease 4, 6.