Parathyroid Hormone (PTH), Intact

Overview

Parathyroid hormone (PTH), intact, is a critical peptide hormone secreted by the parathyroid glands that regulates calcium and phosphate balance in the body. It primarily acts on bones, kidneys, and the small intestine to maintain serum calcium levels within a narrow range essential for nerve, muscle, and cardiac function. Measuring intact PTH levels helps diagnose and monitor disorders of calcium metabolism such as hyperparathyroidism, hypoparathyroidism, and chronic kidney disease-related mineral imbalances.

Scientific Background

PTH is synthesized as a 115-amino acid precursor and processed to the biologically active 84-amino acid intact hormone. It is secreted by the chief cells of the parathyroid glands in response to low blood calcium. PTH increases serum calcium by stimulating osteoclast-mediated bone resorption, enhancing renal calcium reabsorption, and promoting activation of vitamin D (calcitriol) in the kidneys, which increases intestinal calcium absorption. The hormone acts mainly through the parathyroid hormone 1 receptor (PTH1R) found in bone and kidney tissues. Intact PTH has a short half-life of about 4–5 minutes. In circulation, PTH is metabolized into inactive fragments, primarily cleared by the kidneys, which can accumulate in renal failure, complicating interpretation of total PTH levels.

Measurement and Testing

Intact PTH is measured in blood using immunoassays that specifically detect the full-length 1-84 amino acid molecule, distinguishing it from inactive fragments. Testing is typically performed alongside serum calcium and phosphate to assess parathyroid function and calcium metabolism. Factors such as kidney function, vitamin D status, and recent calcium intake can affect PTH levels. Testing is recommended when calcium abnormalities are detected or in conditions like osteoporosis, kidney disease, or suspected parathyroid disorders.

Reference Ranges

Standard reference ranges for intact PTH vary by laboratory but generally fall between 10 to 65 pg/mL. These ranges may differ based on assay methods and population demographics. Levels tend to be higher in older adults and in individuals with reduced kidney function due to decreased clearance of PTH fragments. Interpretation must consider concurrent calcium, phosphate, and vitamin D levels to accurately assess parathyroid gland activity and calcium homeostasis.

High Values

Elevated intact PTH levels can result from primary hyperparathyroidism (overproduction by parathyroid glands), secondary hyperparathyroidism (compensatory increase due to low calcium or vitamin D deficiency), or tertiary hyperparathyroidism (autonomous secretion after prolonged secondary hyperparathyroidism, often in chronic kidney disease). High PTH causes hypercalcemia, bone resorption leading to osteoporosis, kidney stones, and neuromuscular symptoms such as weakness and fatigue.

Low Values

Low intact PTH levels are typically seen in hypoparathyroidism, which may be due to surgical removal or damage to the parathyroid glands, autoimmune destruction, or genetic causes. This leads to hypocalcemia, causing symptoms like muscle cramps, tetany, seizures, and cardiac arrhythmias. Low PTH can also be observed in conditions of magnesium deficiency or in rare cases of parathyroid hormone resistance.

Improving Biomarker Levels

Management to normalize PTH levels depends on the underlying cause. For high PTH due to vitamin D deficiency or chronic kidney disease, vitamin D supplementation and phosphate control are key. Primary hyperparathyroidism may require surgical removal of overactive glands. For low PTH, calcium and active vitamin D analog supplementation are standard. Lifestyle modifications include adequate dietary calcium and vitamin D intake, avoiding excessive phosphate, and managing kidney health. Supplementation should be guided by healthcare providers to avoid complications.

Importance of Tracking

Monitoring intact PTH levels is essential for diagnosing and managing disorders of calcium metabolism, guiding treatment decisions, and preventing complications such as bone disease and cardiovascular issues. Regular tracking is particularly important in patients with chronic kidney disease, osteoporosis, or after parathyroid surgery to ensure optimal calcium balance and bone health.

References

1. Parathyroid hormone - Wikipedia
2. Mayo Clinic Labs: Parathyroid Hormone, Serum
3. MedlinePlus: Parathyroid Hormone (PTH) Test
4. StatPearls: Physiology, Parathyroid Hormone
5. Cleveland Clinic: Parathyroid Hormone

Disclaimer

The information provided in this document is for educational purposes only and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.