Calcium Tests: Serum, Ionized Calcium, Albumin Correction and Parathyroid Hormone
How total calcium, ionized calcium, albumin-adjusted calcium, urine calcium and parathyroid hormone tests work together, what results can mean, and why a clinician interprets them.
Content last updated . This page has not been medically reviewed.
Seek care first
Very low or very high blood calcium can be serious. MedlinePlus lists irregular heartbeat and, if levels are extremely low, seizures among symptoms of low calcium, and constipation, nausea, thirst, frequent urination, kidney stones, fatigue and confusion among symptoms of high calcium. [1] Many people with abnormal calcium have no symptoms. [1] Seek emergency care for seizures, fainting or chest pain (in the US, call 911). Do not start or stop calcium or vitamin D on your own because of a result; ask the clinician who ordered the test.The short answer
A calcium blood test measures how much calcium is in your blood, and about 1% of the body's calcium is there; the rest is in bones and teeth. [1] Your parathyroid glands and hormones keep blood calcium within a narrow range, so an abnormal result can point to a problem with those controls, vitamin D, the kidneys or absorption, as well as to diet. [2][3][1] A clinician reads calcium together with other tests.Total calcium, ionized calcium and albumin
- Total calcium measures all calcium in the blood, part attached to proteins (bound) and part free. It is the most common test and is often part of a basic or comprehensive metabolic panel. [1][4]
- Ionized calcium measures only free calcium, the form active in the body. It is harder to do, so it is usually ordered when total calcium is not normal, or in people who are seriously ill or having surgery. [1]
- How the two relate. Normally the body tightly controls the balance of bound and free calcium, so total calcium gives a good estimate of ionized calcium. [1] Low blood protein, which can come from liver disease or malnutrition, is listed among causes of a lower total calcium result. [1]
- Albumin correction. Labs and clinicians sometimes adjust total calcium for albumin (a blood protein) using a formula. We did not read a source giving a validated formula for general use, so none is shown here. A 2026 intensive care study of 250 patients found that no simple albumin-correction formula significantly outperformed unadjusted total calcium for detecting low ionized calcium, and noted that adjusted calcium is widely used despite uncertainty about its accuracy in critically ill adults. [5] That study was in intensive care and may not apply to healthy people.
Parathyroid hormone (PTH)
The parathyroid glands make PTH when blood calcium gets too low, and PTH raises it again. [2] A PTH test is most often used to find out whether a parathyroid problem is behind an abnormal calcium result. [3] Your provider reads PTH together with calcium. [3]| Calcium | PTH | What it may mean (per MedlinePlus) |
|---|---|---|
| High | High | Primary hyperparathyroidism; a benign growth (adenoma) on a parathyroid gland is the most common cause of high PTH [3] |
| Low | High | Secondary hyperparathyroidism: the glands are working and trying to raise calcium. Causes include low vitamin D, phosphate or magnesium; not getting enough calcium; digestive disorders that limit absorption; and kidney failure [3] |
| Low | Low | Hypoparathyroidism: damage from neck surgery or radiation, autoimmune disorders, some genetic disorders, or too much vitamin D and/or calcium from supplements or antacids [3] |
This table is a simplification; many other patterns exist and only a clinician can interpret yours.
Calcium in urine
A 24-hour urine test collects all urine for a day. [2] It is used with other tests to diagnose kidney stones, to look at how the parathyroid glands are working, and to find the cause of abnormal blood calcium. [2] Higher urine calcium can accompany kidney stones or overactive parathyroid glands, and lower urine calcium can accompany kidney disease, low vitamin D or magnesium, malabsorption and malnutrition. [2] Diet (for example a lot of sodium), supplements and medicines such as antacids and some diuretics can change the result. [2]What common causes of abnormal results look like
- Higher than normal total calcium: overactive parathyroid glands, some cancers including cancer that has spread to bone, bone disorders such as Paget's disease, and taking too much vitamin D over a long period. [1]
- Lower than normal total calcium: low blood protein, underactive parathyroids, too little calcium in the diet, too little vitamin D or magnesium, pancreatitis and kidney disease. [1]
What these tests cannot show
A calcium blood test does not tell you how much calcium is in your bones; bone density is measured with a bone density (DEXA) scan. [1] An abnormal result does not always mean a condition that needs treatment. [1] See Osteoporosis and Bone Health.Frequently asked questions
What is the difference between total and ionized calcium?
Total calcium counts all calcium in the blood. Ionized calcium counts only the free, active portion and is usually ordered when total calcium is abnormal or a person is seriously ill. [1]
Do I need an albumin-corrected calcium?
That is a clinician's decision. In a 2026 intensive care study, no simple correction formula beat the unadjusted total calcium, so the benefit of adjustment is uncertain in very sick patients. [5]
Why was PTH ordered with my calcium?
PTH helps show whether the parathyroid glands are behind an abnormal calcium result. [3]
Can a calcium blood test show if my bones are weak?
No. It does not measure calcium in bones; a bone density scan does. [1]
Can vitamin D or calcium pills change these results?
Yes. Too much vitamin D over a long time can raise blood calcium, and too much from supplements is listed as a cause of low PTH. [1][3]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: established nutritional role / deficiency treatment, insufficient evidence.
Safety
- Supplements can cause the problem you are testing for. Too much vitamin D over a long time can raise blood calcium, and too much vitamin D or calcium from supplements or calcium-containing antacids is listed as a cause of low PTH. [1][3] Tell your clinician about every supplement; see Vitamin D Deficiency and Testing.
- Medicines. Do not stop any medicine unless your provider tells you to. [1] See Medication Interactions.
- Kidney disease, pregnancy, children and older adults. Each changes how calcium is handled; ask a clinician or pharmacist before using calcium or vitamin D products. See Calcium and Calcium Deficiency and Low Blood Calcium.
References
- MedlinePlus, Calcium Blood Test. Read 2026-10-23.
- MedlinePlus, Calcium in Urine Test. Read 2026-10-23.
- MedlinePlus, Parathyroid Hormone (PTH) Test. Read 2026-10-23.
- MedlinePlus, Basic Metabolic Panel (BMP). Read 2026-10-23.
- Limited diagnostic utility of albumin-corrected calcium in the intensive care unit. PLoS One 2026. PubMed. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.