Parathyroid Hormone (PTH), Intact
A hormone from four small glands in your neck that keeps your blood calcium steady. It is read together with calcium and vitamin D.
AI-verified against cited sources. Awaiting expert reviewAlso called PTH, iPTHLOINC 2731-8
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What it is
Parathyroid hormone (PTH) is made by four small glands in your neck. When blood calcium drops, the glands release more PTH. It tells your bones to release calcium, helps your gut absorb it and helps your kidneys hold on to it. When calcium is high, PTH should fall. That is why PTH is almost always read together with a calcium level. This test measures 'intact' PTH.
Why it matters
PTH helps explain an unusual calcium or phosphate level, and it is a key test for parathyroid problems, vitamin D deficiency and kidney disease. On its own, a high or low PTH means little. What matters is whether it fits your calcium. A PTH inside the usual range can still be too high for a high calcium level.
If it’s low
A PTH below your lab's range means your parathyroid glands are releasing less hormone than usual. If your calcium is low too, the glands may not be making enough PTH (hypoparathyroidism). If your calcium is high, a low PTH suggests the extra calcium is coming from something other than the parathyroid glands.
Common causes
- Damage to or removal of parathyroid tissue during neck surgery, such as thyroid surgery, or from radiation to the neck
- Autoimmune disease that attacks the parathyroid glands
- Too much calcium or vitamin D from supplements or calcium-containing antacids
- Low magnesium in the blood
- Serious illness
- Some cancers that raise blood calcium, including cancers that spread to bone
- A genetic condition such as DiGeorge syndrome (22q11.2 deletion)
What can help
- Ask your clinician whether calcium, magnesium and vitamin D should be checked
- If you've had neck surgery, ask how often your calcium and PTH should be checked
If it’s high
A PTH above your lab's range means your parathyroid glands are releasing more hormone than usual. Whether the glands are the cause or are responding to something else depends on your blood calcium. High PTH with high calcium is linked to an overactive gland (primary hyperparathyroidism). High PTH with low or normal calcium often means the body is reacting to low calcium, low vitamin D or kidney disease (secondary hyperparathyroidism).
Common causes
- Low vitamin D, not enough calcium from food, or trouble absorbing it
- Chronic kidney disease
- A benign growth (adenoma) on one parathyroid gland, the most common cause of primary hyperparathyroidism
- Enlarged parathyroid glands (hyperplasia)
- Digestive conditions or weight-loss surgery that reduce calcium and vitamin D absorption
- Pregnancy or breastfeeding (uncommon)
- Lithium or thiazide water pills, which can raise calcium and look like primary hyperparathyroidism
- A rare inherited condition, such as familial hypocalciuric hypercalcemia
- Parathyroid cancer (rare)
What can help
- Ask your clinician whether calcium, vitamin D, phosphate, magnesium and kidney function should be checked or rechecked with this result
- Ask whether a repeat PTH, drawn at a similar time of day and alongside calcium, would be useful
- If your calcium is low or normal, ask your clinician whether your calcium and vitamin D intake are enough
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 18–59 pg/mL. Source: ARUP Laboratories, U.S. Food and Drug Administration.
- 18+ (this one applies)18–59 pg/mL
Sources: ARUP Laboratories, U.S. Food and Drug Administration
If this applies to you
PTH means a little more for some people. Open the one that fits you.
Had weight-loss surgery
PTH is the hormone that keeps blood calcium steady. When calcium and vitamin D absorption fall, PTH can rise to hold calcium up, so it is read with calcium and vitamin D. BOMSS suggests checking PTH after surgery if it wasn't checked before, to rule out an overactive parathyroid gland, and calcium at 3, 6 and 12 months, then at least yearly.
Kidney disease or at risk
PTH (parathyroid hormone) keeps blood calcium steady. KDIGO 2024 notes that PTH, calcium and phosphorus start to change early in CKD and change more as eGFR falls, so PTH is read together with the other two.
Taking lithium
PTH is the hormone from the parathyroid glands that controls calcium. Long-term lithium is linked to a lasting rise in PTH along with high calcium, so PTH is often read alongside a raised calcium.
What can affect your result
- Blood calcium and vitamin D: PTH goes up when either is low
- Time of day: PTH follows a daily rhythm and rises at night
- Age: levels tend to rise gradually over the years
- Sex: women tend to run slightly higher than men
- Season: levels tend to be higher in winter, when vitamin D is lower
- Kidney function
- How the sample is handled, because PTH breaks down quickly
- The assay, since different PTH methods can give noticeably different results
- PTH breaks down quickly in the tube. Labs ask for EDTA plasma, or for serum that is spun down right away, and keep samples cold or frozen.
- Time of day: intact PTH follows a daily rhythm and rises at night, so drawing at a similar time of day makes repeat tests easier to compare. Some clinicians ask for a morning fasting sample.
- Calcium or vitamin D supplements taken in large amounts, and calcium-containing antacids, can lower PTH.
- Immunoassays can be thrown off by heterophile antibodies. Quest reports that its assay is not affected by biotin; ask your lab about its own method.
- Grossly hemolyzed samples are rejected by labs such as Quest and ARUP.
- Different PTH assays give different results, and some read differently in serum than in EDTA plasma. Use the same lab when you compare results over time.
Responds within minutes to a change in blood calcium, because PTH has a half-life of only about 3 to 5 minutes.
When to talk to a clinician
A PTH result is rarely an emergency on its own. See a clinician soon if your PTH is high along with a high calcium and you have symptoms such as strong thirst, urinating more than usual, kidney stones, bone or muscle aches, constipation or confusion. Seek care promptly for muscle cramps or spasms, tingling around the mouth or in the fingers, or an irregular heartbeat, which can go with low calcium. If you have a seizure, chest pain, trouble breathing or fainting, call 911 or your local emergency number.
Questions you could ask
- Which lab and PTH test should I use each time so my results can be compared?
- Does my PTH fit with my calcium and vitamin D levels?
- Could low vitamin D, low calcium intake or my kidney function explain this?
- Should we repeat it, and would any other tests help explain it?
- Is my calcium also low, and should magnesium and vitamin D be checked?
- Could this be related to past neck surgery or to a medicine or supplement I take?
Questions people ask
Why does my clinician want calcium checked with my PTH?
PTH's job is to keep calcium steady, so each result makes sense only next to the other. A PTH that looks normal can still be too high for a high calcium level.
Does vitamin D affect my PTH?
Yes. When vitamin D is low, the gut absorbs less calcium, and PTH rises to make up for it. Some PTH ranges, such as the one ARUP prints, describe people whose vitamin D is in a good range. If PTH is high, clinicians often check vitamin D too.
How do I convert PTH from pg/mL to pmol/L?
Multiply pg/mL by 0.106 to get pmol/L. For example, 59 pg/mL is about 6.3 pmol/L. To go the other way, multiply pmol/L by 9.4. Different PTH assays give different numbers, so compare results from the same lab.
Show the science and sources
Units
- 1 pg/mL = 1 pg/mL
- 1 pg/mL = 0.1061 pmol/L
Is a change real?
PTH naturally varies about 14.7% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 42% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
PTH is an 84-amino-acid peptide (about 9.4 kDa) with a blood half-life of roughly 3 to 5 minutes (Khan 2017). Second-generation 'intact' immunoassays pair an N-terminal and a C-terminal antibody. They also recognize large fragments such as PTH(7-84), which build up as kidney function falls, while third-generation 'bio-intact' assays target PTH(1-84) only (see PTH, bio-intact). Method comparability is poor: recognition of PTH(7-84) varies up to about 3-fold between assays, and some assays give different results in serum than in EDTA plasma (Sturgeon 2011). PTH is unstable in unseparated serum, so labs prefer EDTA plasma or serum that is separated quickly (Quest, ARUP). For that reason KDIGO 2017 states dialysis targets as roughly 2 to 9 times the assay's upper normal limit rather than as an absolute number, and recommends basing decisions in CKD G3a-G5D on trends rather than a single value. Typical adult intervals differ by lab and over time: 18-59 pg/mL at ARUP (set in people with normal calcium and phosphate and optimal vitamin D), close to the 17.9-58.6 pg/mL Roche reported to the FDA for its Elecsys PTH assay; 15-65 pg/mL (1.6-6.9 pmol/L) on an earlier Roche Cobas setup; and 10-65 pg/mL from MedlinePlus. Normocalcemic primary hyperparathyroidism is diagnosed when intact PTH is high with normal albumin-adjusted and ionized calcium on at least two occasions over 3 to 6 months, after secondary causes are excluded. After thyroidectomy, a PTH above 10 pg/mL (1.05 pmol/L) measured 12 to 24 hours after surgery virtually excludes long-term hypoparathyroidism (Second International Workshop, 2022). In a large retrospective data set, PTH rose gradually with age, was higher in women, and moved opposite to 25(OH)D across the seasons (Serdar 2017); intact PTH also shows a circadian pattern with a rise at night (Calvo 1991). Conversion: pmol/L = pg/mL x 0.106 (molecular weight 9,424.7). No published critical-value limit for PTH was found.
LOINC 2731-8 (primary), 14866-8. Specimen: serum-or-plasma.
Sources
- Parathyroid Hormone, Intact (test 0070346), ARUP Laboratories
- Parathyroid hormone (PTH) blood test, MedlinePlus (National Library of Medicine)
- Parathyroid Hormone (PTH) Test, MedlinePlus (National Library of Medicine)
- Normocalcemic Hyperparathyroidism: Study of its Prevalence and Natural History, Journal of Clinical Endocrinology & Metabolism (2020)
- PTH, Intact without Calcium (test code 35202), Quest Diagnostics
- KDIGO 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD), Kidney International Supplements (2017)
- Primary hyperparathyroidism: review and recommendations on evaluation, diagnosis, and management. A Canadian and international consensus, Osteoporosis International (2017)
- Primary hyperparathyroidism: clinical manifestations, diagnosis and evaluation according to the Fifth International Workshop guidelines, Reumatologia (2023)
- Evaluation and Management of Hypoparathyroidism Summary Statement and Guidelines from the Second International Workshop, Journal of Bone and Mineral Research (2022)
- Variation in parathyroid hormone immunoassay results - a critical governance issue in the management of chronic kidney disease, Nephrology Dialysis Transplantation (2011)
- Analysis of Changes in Parathyroid Hormone and 25 (OH) Vitamin D Levels with Respect to Age, Gender and Season: A Data Mining Study, Journal of Medical Biochemistry (2017)
- Circadian variation in ionized calcium and intact parathyroid hormone: evidence for sex differences in calcium homeostasis, Journal of Clinical Endocrinology & Metabolism (1991)
- UniProtKB P01270 (PTH_HUMAN), parathyroid hormone, UniProt Consortium
- 510(k) Decision Summary: Elecsys PTH and Elecsys PTH STAT (K231927), U.S. Food and Drug Administration
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.