A parathyroid hormone (PTH) result only makes sense next to a calcium result taken at the same time. PTH is the hormone your body uses to keep blood calcium in a narrow range, so a high PTH with high calcium points to a different problem than a high PTH with low calcium. Before the blood draw, it is also worth telling the lab and your clinician if you take biotin supplements, because high-dose biotin can distort some hormone tests.
What PTH does and why calcium is tested with it
PTH is a small peptide hormone. UniProt’s protein record shows the mature hormone is a chain of 84 amino acids made by the parathyroid glands, four pea-sized glands in the neck. MedlinePlus explains that when blood calcium drops, these glands release PTH, which tells bones to release calcium, helps the intestines absorb calcium from food, and helps the kidneys hold on to calcium. When calcium returns to normal, PTH falls. Because the two move together, a calcium test is usually ordered with a PTH test.
The most common reason for the test is an abnormal calcium result on routine blood work. It is also used to investigate low phosphate, monitor chronic kidney disease, look for causes of severe osteoporosis, and check treatment for parathyroid disorders. MedlinePlus says most people need no special preparation, though some providers ask for fasting or a specific time of day.
Reading PTH and calcium together
- High PTH and high calcium usually means primary hyperparathyroidism, where a parathyroid gland is overactive. NIDDK, part of the National Institutes of Health, explains on its primary hyperparathyroidism page that in about 8 of 10 cases the cause is a benign growth called an adenoma. NIDDK also notes that PTH sitting in the upper part of the normal range while calcium is high can be a sign of the condition, because PTH should be low when calcium is high.
- High PTH and low calcium is called secondary hyperparathyroidism. MedlinePlus says the glands are working correctly and responding to a problem elsewhere, such as low vitamin D, low calcium intake, poor absorption from the gut, or kidney failure.
- Low PTH and low calcium suggests hypoparathyroidism, which can follow neck surgery or radiation, autoimmune conditions or genetic disorders.
NIDDK says most people with primary hyperparathyroidism have no symptoms and the condition is often caught early through routine blood tests. It is one of the most common hormonal disorders, affecting women 3 to 4 times as often as men and most often appearing between ages 50 and 60. Low vitamin D is common alongside it, which is why doctors usually check vitamin D too. International guidelines from the Fifth International Workshop on primary hyperparathyroidism (2022) set out evidence-based recommendations for evaluation and management, including when surgery is advised for people without symptoms.
Why biotin supplements matter before a hormone test
Many lab tests, including hormone tests, rely on a biotin-based chemical step. In a small 2017 study in JAMA, six healthy adults took a biotin supplement for a week at a dose the authors describe as common in over-the-counter products, and researchers re-ran 37 tests for 11 substances, including PTH, thyroid hormones and NT-proBNP. Interference appeared in 9 of the 23 biotin-based tests, giving falsely high results on some and falsely low on others, while none of the 14 tests without biotin components were affected. The authors said this should be considered before ordering blood tests for people taking biotin. The NIH Office of Dietary Supplements likewise warns that biotin above recommended amounts may cause false results in some lab tests that measure hormones.
Questions to ask about your result
- What was my calcium at the same time, and has it been abnormal more than once?
- Has my vitamin D and kidney function been checked?
- Could a multivitamin, B-complex or biotin-only supplement have affected this result?
- Do I need a bone density scan or a kidney check for stones?
The takeaway: keep your PTH and calcium results side by side, list every supplement you take when tests are ordered, and ask whether any biotin-containing product should be paused before a repeat test. Don’t start or stop calcium or vitamin D supplements to “fix” a number without talking to your clinician.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-05 PT). Not medical advice.
Sources
- MedlinePlus (U.S. National Library of Medicine): Parathyroid Hormone (PTH) Test
- NIDDK (National Institutes of Health): Primary Hyperparathyroidism
- Bilezikian JP, et al. Evaluation and Management of Primary Hyperparathyroidism: Summary Statement and Guidelines from the Fifth International Workshop. Journal of Bone and Mineral Research, 2022.
- Li D, et al. Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults. JAMA, 2017.
- NIH Office of Dietary Supplements: Biotin Fact Sheet for Consumers
- UniProt: P01270, Parathyroid hormone (human)