Nursing care
Parathyroid Hormone: reading the number and acting on it
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated September 2026
Short answer
Parathyroid hormone (PTH) regulates blood calcium by acting on bone, kidney and gut. The number alone doesn't diagnose anything — pair it with the calcium. High PTH with high calcium points to primary hyperparathyroidism; high PTH with low calcium points to the kidneys failing to activate vitamin D and retain calcium.
What the test measures
PTH is released by the four parathyroid glands in response to falling serum calcium. It raises calcium by pulling it from bone, increasing renal reabsorption, and activating vitamin D to boost gut absorption. The lab usually reports intact PTH, drawn alongside a serum calcium and often phosphate.
Because PTH and calcium move in a tight feedback loop, ordering one without the other tells you very little. A nurse reading a PTH result in isolation is reading half the story. Always pull the paired calcium before interpreting the number, and check the timing — PTH has a short half-life and is affected by the time of day the sample was drawn.
Normal ranges and what moves them
Intact PTH typically runs 10 to 65 pg/mL, though the reference range varies by lab and assay, so check the local range printed on the report rather than quoting a fixed figure. Values shift with age, vitamin D status, renal function and even the time of the draw, since PTH follows a mild diurnal pattern.
Low magnesium blunts PTH secretion even when calcium is low, so a patient on a proton pump inhibitor long-term or with poor intake can show an inappropriately low PTH. Renal impairment does the opposite: as glomerular filtration falls, phosphate retention and reduced vitamin D activation drive PTH up as a compensatory response, not a gland problem.
What a high result means
This is where the calcium does the differentiating. High PTH with high calcium is primary hyperparathyroidism — usually a solitary adenoma oversecreting PTH despite calcium already being adequate. The gland has stopped responding to the feedback loop.
High PTH with low or low-normal calcium is a different disease entirely: secondary hyperparathyroidism, most often from chronic kidney disease. Here the parathyroid glands are working correctly — they are pushing out more hormone because the kidneys cannot activate vitamin D or retain calcium, so the gland is compensating for someone else's failure. Confusing the two leads to the wrong intervention, since one needs a parathyroidectomy and the other needs renal and vitamin D management.
What a low result means
Low PTH with low calcium is hypoparathyroidism, most commonly iatrogenic after thyroid or neck surgery where a parathyroid gland was inadvertently removed or devascularized. Watch for it in any post-thyroidectomy patient, particularly in the first 24 to 48 hours.
Low PTH with high calcium points away from the parathyroid gland altogether. Suspect malignancy-related hypercalcemia, where a tumour secretes PTH-related peptide (PTHrP) that mimics PTH's action on bone and kidney but suppresses the parathyroid glands' own output through the normal feedback loop. The two conditions look similar on a calcium panel but need an entirely different workup.
Nursing actions by result
For suspected primary hyperparathyroidism, anticipate imaging (sestamibi scan or neck ultrasound) to localise the adenoma before surgical referral, and monitor for the classic hypercalcemia picture: constipation, polyuria, fatigue, and shortened QT interval on ECG. Encourage hydration to support renal calcium clearance while the workup proceeds.
For a post-thyroidectomy patient with a falling PTH, watch closely for perioral tingling, muscle twitching and a positive Chvostek's or Trousseau's sign — early signs of tetany from dropping calcium. Keep IV calcium gluconate accessible and recheck calcium levels per protocol until the trend stabilises.
Patient preparation and teaching
No fasting is required for PTH, but draw it in the morning where possible since levels vary through the day, and note the exact draw time on the request if the lab asks for it. Confirm current medications, since lithium and thiazide diuretics can raise PTH independent of any gland pathology.
Tell the patient this test looks at how their body manages calcium, not at the thyroid, even though the glands sit near it. If they are being worked up for hyperparathyroidism, explain that a scan to find the affected gland usually follows before any decision about surgery is made.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our endocrine practice questions are the closest set to what this page covers.
Common questions
Why do you need both PTH and calcium to interpret the result?
PTH and calcium regulate each other in a feedback loop, so the same PTH number means different things depending on the calcium. A high PTH with high calcium is the gland overworking; a high PTH with low calcium is the gland compensating for someone else's problem, usually the kidneys.
What's the difference between primary and secondary hyperparathyroidism?
Primary means the parathyroid gland itself is autonomously oversecreting PTH, usually from an adenoma, and calcium runs high. Secondary means the gland is responding appropriately to a real calcium deficit, most often from chronic kidney disease, so PTH is high but calcium is low or low-normal.
What should a nurse watch for after thyroid surgery?
Watch for signs of hypocalcemia from accidental parathyroid injury or removal: perioral tingling, muscle twitching, and Chvostek's or Trousseau's sign. PTH and calcium are typically trended in the first 24 to 48 hours postoperatively.
Does magnesium affect PTH results?
Yes. Significant hypomagnesemia suppresses PTH release even when calcium is low, producing a PTH result that looks inappropriately normal or low. Correct magnesium before relying on a PTH level in a patient with poor intake or on long-term acid-suppressing therapy.