The Parathyroid Hormone (PTH – Intact) test is a blood test that measures the level of intact PTH (the full, biologically active form of parathyroid hormone) in your bloodstream. PTH is made by four small glands in your neck called the parathyroid glands. Despite the similar name, these are different from the thyroid gland.

PTH is one of the main hormones responsible for calcium balance in the body. It helps regulate:

• Blood calcium levels (raising calcium when it’s low)
• Phosphate levels
• Vitamin D activation (which affects calcium absorption from food)
• Bone remodeling (the normal process of bone breakdown and rebuilding)

This test is most helpful when interpreted along with other labs—especially blood calcium (total and/or ionized), phosphorus, vitamin D, magnesium, and kidney function tests (creatinine/eGFR). Together, these results help your clinician determine whether symptoms or abnormal calcium levels are coming from the parathyroid glands, the kidneys, vitamin D status, or other causes.

In plain language: if your calcium is abnormal, PTH helps explain why. A high PTH may mean your parathyroid glands are overactive, or that your body is trying to compensate for low calcium or low vitamin D. A low PTH may mean the parathyroid glands are underactive or suppressed (often when calcium is high). “Normal” PTH isn’t always normal—if calcium is high, PTH should usually be low; if it isn’t, that can point to a parathyroid problem.

Doctors commonly order an intact PTH test to evaluate parathyroid function and to investigate problems related to calcium balance, bone health, and kidney health. It’s often ordered when calcium is found to be high or low on routine bloodwork, or when symptoms suggest a calcium disorder.

Your clinician may recommend a PTH test if you have:

Symptoms of high calcium (hypercalcemia), such as increased thirst and urination, constipation, nausea, abdominal pain, fatigue, muscle weakness, “brain fog,” mood changes, or kidney stones.

Symptoms of low calcium (hypocalcemia), such as tingling around the mouth or in the hands/feet, muscle cramps or spasms, twitching, numbness, or—in more severe cases—seizures or abnormal heart rhythms.

Bone and mineral concerns, including osteoporosis or low bone density, frequent fractures, bone pain, or unexplained changes on bone imaging.

Kidney-related concerns, such as chronic kidney disease (CKD), kidney stones, or abnormal phosphorus levels. In CKD, PTH may rise as the body tries to keep calcium and phosphorus in balance (a condition often called secondary hyperparathyroidism).

Risk factors or clinical situations where monitoring is important, including known or suspected parathyroid disease, vitamin D deficiency, malabsorption conditions, or after neck surgery that might affect the parathyroid glands.

Because PTH levels can change with calcium intake, vitamin D status, magnesium levels, and kidney function, clinicians typically interpret this test in context rather than as a stand-alone number.

• Primary hyperparathyroidism (often due to a parathyroid adenoma; commonly causes high calcium with non-suppressed/high PTH)
• Secondary hyperparathyroidism (commonly from chronic kidney disease or vitamin D deficiency; PTH elevated as compensation)
• Tertiary hyperparathyroidism (long-standing secondary hyperparathyroidism, usually in advanced kidney disease)
• Hypoparathyroidism (low PTH leading to low calcium; can occur after thyroid/neck surgery or autoimmune disease)
• Hypercalcemia of malignancy (high calcium typically with low PTH due to suppression)
• Vitamin D deficiency or insufficiency (can raise PTH and affect calcium absorption)
• Chronic kidney disease–mineral and bone disorder (CKD-MBD)
• Osteoporosis/osteopenia related to abnormal calcium and PTH regulation
• Nephrolithiasis (kidney stones) associated with calcium metabolism issues
• Magnesium imbalance (low magnesium can impair PTH secretion and cause low calcium)

• Clarifying the cause of abnormal calcium (distinguishing parathyroid-related vs. non-parathyroid causes of high/low calcium)
• Supporting bone health goals (evaluating contributors to osteoporosis, fractures, and bone density loss)
• Kidney health monitoring in chronic kidney disease (tracking mineral balance and CKD-related bone and mineral disorders)
• Vitamin D optimization and assessing whether low vitamin D is driving an elevated PTH
• Reducing kidney stone risk by identifying calcium metabolism issues that may contribute to stone formation
• Post-surgery follow-up after thyroid/parathyroid procedures (checking for hypoparathyroidism or persistent hyperparathyroidism)
• General metabolic wellness screening when combined with calcium, phosphorus, magnesium, and kidney function tests