Calcium, Serum

Optimal Result: 8.6 - 10.2 mg/dL, or 2.15 - 2.55 mmol/L.

What is Calcium?

Your body requires calcium to maintain healthy bones and teeth. It’s also essential for keeping your nerves, heart, and muscles functioning properly. Since calcium is so important for many of your body’s functions, its levels need to be within a certain range.

Calcium is the most abundant mineral in the body and one of the most important. Our bodies use calcium to build and fix bones and teeth, help nerves work, make muscles contract, aid in blood clotting, and to help our heart beat. That being said, almost all of the calcium in our bodies is stored in the bones (99%). Typically, our bodies carefully regulate the amount of calcium in the bloodstream. When levels are low, our bones release calcium. When levels are too high, our bones absorb the excess calcium or it is excreted through stool and urine. Factors that determine the amount of calcium in your body include: diet, phosphate levels, how much calcium and vitamin D your intestines absorb, and certain hormones (parathyroid hormone, calcitonin, and estrogen). It is critical to get the right amount of calcium in your diet because the human body loses calcium everyday. This is particularly true for pregnant women. The process of creating a baby requires a large amount of calcium. Frequently, the needed calcium will be taken from the mother’s bones during fetal development. This can put mothers at an increased risk for conditions like osteoporosis (brittle bones) in their older age.

Newborns, particularly premature and low birth-weight infants, are often monitored during the first few days of life to determine if their bodies have matured enough to self-regulate calcium levels. An abnormal calcium level may resolve or may require treatment. Most people who have low or high levels of calcium do not start experiencing symptoms until the level becomes very high or very low. 

Although it may be a small amount, the calcium in your blood is essential and does the following:

- Helps your nerves work.

- Helps make your muscles squeeze together so you can move.

- Helps your blood clot if you are bleeding.

- Helps your heart work properly.

The levels of calcium in your blood and bones are controlled by two hormones called parathyroid hormone (PTH) and calcitonin. Vitamin D also plays an important role in maintaining calcium levels because your body needs it in order to absorb calcium.

What is a calcium test?

The total calcium blood test is used to measure the total amount of calcium in your blood. Calcium is one of the most important minerals in your body. Most of your body’s calcium is stored in your bones.

Your doctor will order this test as part of a routine metabolic panel or if you’re experiencing certain symptoms. Be sure to see your doctor if you’re having symptoms of low or high calcium.

A health practitioner may order a calcium test when someone has:

- Kidney disease

- Symptoms of high calcium

- Symptoms of low calcium

- Symptoms of diseases associated with abnormal blood calcium such as:

      → Thyroid disease

      → Parathyroid disorder 

      → Malabsorption

      → Cancer

      → Malnutrition

Your doctor may also order a calcium blood test if they suspect that you have kidney disease, parathyroid disease, cancer, or malnutrition.

It is important to note that blood calcium levels do not reflect the calcium stored in bones, only the calcium circulating in the blood; therefore, a good blood calcium score does not necessarily indicate healthy bones.

What are normal reference ranges for blood calcium levels?

Generally speaking, a normal reference range for the blood total calcium test in adults is between 8.6 and 10.2 milligrams per deciliter (mg/dL). This range can vary from lab to lab.

In order to interpret your individual test results, you should always use the reference ranges provided along with the report of your test results.

Normal Ranges in mg/dL:

0-10 days: 7.6-10.4 

11 days - 2 years: 9.0-11.0 

3-12 yrs: 8.8-10.8 m

>12 yrs: 8.6-10.2  

Note: Laboratories may have different reference ranges for normal blood calcium levels. You shouldn’t compare values from one laboratory to normal ranges from another laboratory.

Abnormal calcium blood levels:

In many cases, high or low results have causes that are easily treated. In other cases, you may need a more complex treatment plan to address the underlying condition. Talk to your doctor about your options. They’ll work to identify and treat the disease or condition that’s affecting your calcium levels.

If you have an abnormal result, your healthcare provider may order additional tests to determine the cause of your abnormal calcium levels. The additional tests may measure your:

- Ionized blood calcium.

- Urine calcium.

- Phosphorus.

- Magnesium.

- Vitamin D.

- Parathyroid hormone (PTH).

- Thyroid hormones.

- Calcitonin.

What is the ionized calcium blood test?

A second calcium blood test, called the ionized calcium blood test, measures the amount of “free” calcium present in your blood. “Free calcium” refers to calcium that’s not bound to any proteins and not together with an anion in your blood.

What is a calcium urine test?

In addition to these two calcium blood tests, the level of calcium in your urine can be measured as well.



Pepe J, Colangelo L, Biamonte F, Sonato C, Danese VC, Cecchetti V, Occhiuto M, Piazzolla V, De Martino V, Ferrone F, Minisola S, Cipriani C. Diagnosis and management of hypocalcemia. Endocrine. 2020 Sep;69(3):485-495. doi: 10.1007/s12020-020-02324-2. Epub 2020 May 4. PMID: 32367335.

de Brito Galvao JF, Schenck PA, Chew DJ. A Quick Reference on Hypocalcemia. Vet Clin North Am Small Anim Pract. 2017 Mar;47(2):249-256. doi: 10.1016/j.cvsm.2016.10.017. Epub 2016 Dec 22. PMID: 28012786.

Garabedian M. Hypocalcemies [Hypocalcemia]. Rev Prat. 1998 Jun 1;48(11):1201-6. French. PMID: 9781172.

Minisola S, Pepe J, Piemonte S, Cipriani C. The diagnosis and management of hypercalcaemia. BMJ. 2015 Jun 2;350:h2723. doi: 10.1136/bmj.h2723. PMID: 26037642.

Turner JJO. Hypercalcaemia - presentation and management . Clin Med (Lond). 2017 Jun;17(3):270-273. doi: 10.7861/clinmedicine.17-3-270. PMID: 28572230; PMCID: PMC6297576.

Saint-Hillier Y. Hypercalcémies: conduite diagnostique et thérapeutique [Hypercalcemia: diagnostic and therapeutic procedures]. Rev Prat. 1989 Apr 13;39(11):924-30. French. PMID: 2655059

What does it mean if your Calcium, Serum result is too high?

Test result values that fall above the reference range are considered high. Having a higher-than-normal blood calcium level is called hypercalcemia.

In the medical world, the prefix “hyper-” means “high” or “too much.” Hypercalcemia means you have higher-than-normal calcium in your blood.

Hypercalcemia can affect anyone at any age, but it’s most common in people assigned female at birth over age 50 (after menopause). In most cases, this is due to an overactive parathyroid gland.

Hypercalcemia affects approximately 1% to 2% of the general population. Most of the cases — about 90% — are due to primary hyperparathyroidism and cancer-related hypercalcemia (hypercalcemia of malignancy).

Most cases of hypercalcemia aren’t life-threatening and many people don’t have any symptoms. Healthcare providers often catch it early from routine blood tests.

Symptoms of high calcium levels can include:

- Abdominal pains

- Bone pain

- Constipation

- Forgetfulness, depression or irritability

- Headaches

- Low appetite

- More frequent urination and thirst

- Muscle aches, weakness, cramping and/or twitches.

- Nausea and vomiting

- Tiredness/Fatigue

If you have hypercalcemia, your doctor will aim to identify and treat the condition that’s causing high calcium levels.

Diseases or conditions that can cause hypercalcemia can include:

- Abnormal heart rhythm (= arrhythmia).

- Adrenal gland failure

- Being bedridden or immobilized for a prolonged period of time

- Breast cancer

- Certain cancers of the blood

- Coma

- Confusion

- Hyperparathyroidism

- Hyperthyroidism (an overactive thyroid gland)

- Kidney failure

- Lung cancer

- Lung diseases such as sarcoidosis and tuberculosis

- Medications such as lithium and thiazide diuretics

- Multiple myeloma

- Paget’s disease of the bone

- Taking too much calcium or vitamin D through supplementation

- Taking too much calcium carbonate (Tums or Rolaids) supplements

If your calcium blood test results reveal that you have high or low levels of calcium, it doesn't necessarily mean that you have a medical condition. Other factors, such as diet and certain medications, can affect your calcium levels. There could’ve also been an error in the collection, transport or processing of the test.

Potential treatment of hypercalcemia:

Treatment of hypercalcemia depends on what’s causing it and how severe it is. In mild cases of hypercalcemia, your healthcare provider may tell you to:

- Drink more water.

- Switch to a non-thiazide diuretic or blood pressure medication.

- Stop taking or lower your dose of calcium-rich antacid tablets.

- Stop taking or lower your dose of calcium supplements and calcium-containing supplements, such as multivitamins.

If the hypercalcemia is due to an overactive parathyroid gland, your provider will most likely recommend surgery to have the overactive parathyroid gland(s) removed.

If the hypercalcemia is severe, and/or causing significant symptoms, your provider may recommend immediate hospitalization for IV fluids and other treatments.

Potential prevention of hypercalcemia:

Not all cases of hypercalcemia can be prevented, but avoiding excess intake of calcium pills and calcium-based antacid tablets can help.

Be sure to talk with your healthcare provider if you have a family history of high calcium, kidney stones or parathyroid conditions. Avoid taking dietary supplements, vitamins or minerals without first discussing them with your provider.

Prognosis of hypercalcemia:

Prognosis, like treatment, depends on the cause and severity of hypercalcemia. When hypercalcemia happens due to a benign (= not harmful) condition or temporary situation, it generally has a good prognosis.

People who have hypercalcemia due to cancer often experience symptoms and require frequent hospitalizations.

Complications of hypercalcemia?

Complications of long-term hypercalcemia are rare since calcium levels are checked in routine blood panels and healthcare providers usually catch hypercalcemia early, but complications can include:

- Calcium deposits in your kidney (nephrocalcinosis) that cause poor kidney function.

- Kidney failure

- Kidney stones

- High blood pressure (hypertension)

- Depression

- Bone cysts

- Bone fractures

- Osteoporosis


Elevated Calcium and (upper-)normal PTH Levels: Potential indicators of Parathyroid and other health conditions:

If intact parathyroid hormone (PTH) levels are in the (upper-)normal range and calcium levels are slightly elevated, it could indicate primary hyperparathyroidism, where one or more parathyroid glands are overactive, although other conditions like Familial Hypocalciuric Hypercalcemia (FHH), medication or supplement effects, and certain medical conditions may also be responsible. These findings should be interpreted in the context of the patient's overall health and symptoms, with further diagnostic tests and consultation with a healthcare provider necessary for an accurate diagnosis and appropriate treatment plan.

What does it mean if your Calcium, Serum result is too low?

When your test result values fall below the reference range, they’re considered low. Having a low blood calcium level is called hypocalcemia.

The prefix “hypo-” means “low” or “not enough.” Hypocalcemia means you have lower-than-normal levels of calcium in your blood.

Typically, hypocalcemia occurs when either too much calcium is lost through your urine or when not enough calcium is moved from your bones into your blood.

Symptoms of low calcium levels include:

- cramps in your abdomen or muscles

- a tingling sensation in your fingers

- irregular heartbeat

Your doctor may treat hypocalcemia through the use of calcium supplements and sometimes vitamin D supplements. If there’s an underlying disease or condition that’s causing your hypocalcemia, they’ll work to identify and treat that as well.

Some of the potential causes of hypocalcemia include:

- Certain medications, including corticosteroids, anticonvulsants, and rifampin (an antibiotic)

- Deficiency of calcium or vitamin D in your diet

- Hypoparathyroidism (an underactive parathyroid gland)

- Increased levels of phosphorus [Elevated phosphate levels also inhibit 1-alpha hydroxylase, a renal enzyme required for activation of Vitamin D. The decrease of active vitamin D results in decreased intestinal absorption of calcium, decreased renal calcium and phosphate reabsorption, and impaired bone mineralization.]

- Inherited resistance to the effects of parathyroid hormone

- Kidney failure [in chronic kidney disease (=CKD), the kidneys are less able to make active vitamin D. Without enough active vitamin D, you absorb less calcium from the food you eat, so it then becomes low in your blood.]

- Low levels of albumin in the blood [possibly due to malnutrition or liver disease, in which the total calcium level may or may not reflect a truly hypocalcemic state. Low albumin levels can also be due to malabsorption syndromes, or malnutrition. Also, low albumin is very common if you are acutely ill. With low albumin, only the bound calcium is low. Ionized calcium remains normal, and calcium metabolism is being regulated appropriately.]

- Magnesium deficiency [Normally, the parathyroid glands release a hormone that increases blood calcium levels when they are low. Magnesium is required for the production and release of parathyroid hormone, so when magnesium is too low, insufficient parathyroid hormone is produced and blood calcium levels are also reduced (hypocalcemia).]

- Pancreatitis (inflammation of the pancreas)

- Problems with absorption of calcium

- Renal failure

If your calcium blood test results reveal that you have high or low levels of calcium, it doesn't necessarily mean that you have a medical condition. Other factors, such as diet and certain medications, can affect your calcium levels. There could’ve also been an error in the collection, transport or processing of the test

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