What this test measures
Parathyroid hormone (PTH) is secreted by the four parathyroid glands behind the thyroid in response to a fall in ionised calcium. PTH raises serum calcium by mobilising it from bone, increasing renal calcium reabsorption, and stimulating renal production of activated vitamin D (which boosts intestinal calcium absorption). PTH falls when calcium is adequate.
"Intact" or "second-generation" PTH assays measure the full-length 1–84 amino acid biologically active hormone in serum. Modern third-generation assays distinguish "whole" PTH (1–84 only) from intact PTH (1–84 plus 7–84 fragments). For most clinical purposes the intact assay is the standard.
Why it matters
PTH is interpreted alongside serum calcium — never alone. Primary hyperparathyroidism (autonomous PTH oversecretion, usually from a parathyroid adenoma) is the commonest cause of an outpatient finding of hypercalcaemia and is fully curable by surgery. India is also seeing a rising tide of nutritional rickets and severe vitamin D deficiency, which raise PTH (secondary hyperparathyroidism) without raising calcium.
In chronic kidney disease, PTH rises progressively as kidneys fail (KDIGO recommends targets that vary by CKD stage). Persistent severe rises can lead to tertiary hyperparathyroidism with high calcium and bone disease. PTH is also low in hypoparathyroidism (post-thyroidectomy, autoimmune, congenital DiGeorge syndrome) — patients need lifelong calcium and active vitamin D.
How to prepare
Fasting is not strictly required but a morning sample on an empty stomach reduces variability. Avoid biotin for 48–72 hours. Sample is best collected in EDTA tube on ice and processed quickly — PTH is unstable at room temperature. Take your usual medications unless your doctor instructs otherwise. Mention any calcium, vitamin D, lithium, thiazide or PPI use — all can affect interpretation.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Intact Parathyroid Hormone (pg/mL)[1][2] | 15 – 65 pg/mL (adult, assay-dependent) | Low PTH with low calcium = hypoparathyroidism (post-thyroidectomy, autoimmune, DiGeorge). Low PTH with high calcium = non-PTH-mediated hypercalcaemia — malignancy (PTH-related peptide), excess vitamin D, sarcoidosis, milk-alkali syndrome. | High PTH with high calcium = primary hyperparathyroidism (parathyroid adenoma — refer for surgery). High PTH with low or low-normal calcium = secondary hyperparathyroidism — vitamin D deficiency (extremely common in India), chronic kidney disease, malabsorption. Very high PTH with high calcium and CKD = tertiary hyperparathyroidism. |
PTH + Calcium — paired interpretation
| Calcium | PTH | Likely diagnosis | Action |
|---|---|---|---|
| High | High | Primary hyperparathyroidism | Sestamibi / neck USG + parathyroidectomy |
| High | Low / suppressed | Non-PTH hypercalcaemia (malignancy, vit D excess) | PTHrP, vitamin D metabolites, imaging |
| Low / low-normal | High | Vitamin D deficiency / CKD / malabsorption | Replete vitamin D; treat cause |
| Low | Low | Hypoparathyroidism | Calcium + active vitamin D replacement |
| Normal | High | Normocalcaemic primary hyperparathyroidism or vit D deficiency | Treat vit D; reassess |
Frequently asked questions
Why is PTH always interpreted with calcium?
PTH on its own is hard to make sense of — the same PTH value means very different things at different calcium levels. The pair tells the story: high calcium + high PTH is primary hyperparathyroidism, while low calcium + high PTH is secondary (usually vitamin D deficiency in India).
My PTH is high but my calcium is normal — what does that mean?
Most often, vitamin D deficiency — extremely common in India. The PTH rises to compensate for low vitamin D before calcium falls. Repleting vitamin D usually normalises PTH within 2–3 months. If PTH stays raised after vitamin D is adequate, "normocalcaemic primary hyperparathyroidism" is considered.
My doctor said I have a parathyroid adenoma — is surgery the only option?
Surgical removal (parathyroidectomy) is curative and is the standard for symptomatic primary hyperparathyroidism, or asymptomatic cases meeting Endocrine Society criteria (calcium > 1 mg/dL above upper limit, low bone density, age < 50, kidney stones, eGFR < 60). Mild asymptomatic disease can be monitored.
I have CKD — what is the target PTH?
KDIGO suggests PTH should be kept within 2 to 9 times the upper limit of normal in CKD stage 5 / dialysis patients. The aim is to suppress excess PTH without over-suppressing it, which causes adynamic bone disease.
Will lithium or thiazide diuretics affect my PTH?
Yes — both can mildly raise PTH and calcium. If a raised calcium is being investigated, stopping the drug for a few weeks and repeating is sometimes recommended.
How should the PTH sample be handled?
PTH is unstable at room temperature. Best practice is collection in an EDTA tube, kept on ice, separated and frozen within an hour. A poorly handled sample can give a falsely low value.
My PTH is undetectably low after thyroid surgery — what now?
Post-thyroidectomy hypoparathyroidism is a recognised complication when parathyroid glands are damaged or removed. You need calcium plus active vitamin D (calcitriol or alfacalcidol) — sometimes lifelong. PTH is monitored every 3–6 months.
Related Hormones / Endocrine tests
Tests commonly ordered alongside INTACT PARATHYROID HORMONE (PTH), or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Primary Hyperparathyroidism Guideline · accessed 2026-05-30T00:00:00.000Z
- KDIGO — CKD-MBD Guideline · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Parathyroid Hormone Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Parathyroid Hormone · accessed 2026-05-30T00:00:00.000Z
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