Hypocalcemia: Symptoms, Causes, and Treatment

Medically Reviewed by Jabeen Begum, MD on June 20, 2024
Written by Kim Painter
8 min read

Hypocalcemia is when you have too little calcium in your blood. It's usually caused by other health conditions.

Calcium is a mineral you need for healthy, strong bones and teeth. But the calcium outside your bones, in your bloodstream, plays a key role in many other body functions, including blood vessel tightening and relaxation, nerve impulses, blood clotting, and muscle contractions.‌

Most of the time, your body tightly controls your calcium levels, using signals from three hormones: parathyroid hormone (PTH), calcitonin, and vitamin D. It's unclear how common low calcium blood levels are. But if you have hypocalcemia, it's important to treat it because of the health problems it can cause.

Hypocalcemia ranges

With a calcium blood test, you can find out if you have low calcium levels. For adults, a normal range is usually 8.5 to 10.2 milligrams/deciliter (2.15 to 2.55 millimoles/liter), though some labs use different ranges. Normal levels are slightly higher in children and teens. If your blood calcium level is higher than normal, you have hypercalcemia; if it's less than normal, that's hypocalcemia.

Usually, hypocalcemia happens when you pee out too much calcium or when your bones release too little calcium into your blood.

The main causes include:

Hypoparathyroidism. The parathyroids are four pea-sized glands found behind the thyroid gland in your neck. The parathyroids make parathyroid hormone ( PTH), which regulates the amount of calcium in your body, partly by telling your bones how much to release into your blood. When you make lower levels of PTH than you need (hypoparathyroidism), your blood calcium levels drop. This might happen when the parathyroid glands get damaged, which can result from thyroid surgery or autoimmune disease — where your immune system attacks your glands or the proteins that sense calcium.

Vitamin D deficiency. Vitamin D, which you can get from food and supplements, and as a result of sun exposure, helps your body absorb calcium. When you don't get enough vitamin D, your blood calcium levels can drop. Some people have a genetic disorder that causes low vitamin D levels.

Chronic kidney disease or kidney failure. When your kidneys don't work well, your body has trouble using vitamin D. Also, high levels of a mineral called phosphorus can build up in your blood. Those problems can drive down your blood calcium levels, even while raising your levels of parathyroid hormone.

Other causes can include:

Pseudohypoparathyroidism. This is a genetic disorder where your body cannot react to PTH. Your body acts like you don't have enough PTH, so you can develop hypocalcemia.

Missing or poorly developed parathyroid glands. This can happen with certain conditions present at birth, such as DiGeorge syndrome, which is a chromosomal disorder.

Abnormal magnesium levels. When you have too much or too little magnesium in your body, calcium levels can drop.

Calcium deficiency. If you do not consume enough calcium or have disorders that interfere with your body’s ability to absorb calcium, it can cause hypocalcemia.

Pancreatitis. An inflamed pancreas, most often linked to heavy alcohol use or gallstones, can cause low blood calcium levels.

Certain medications. Drugs such as rifampin (an antibiotic) as well as phenytoin and phenobarbital (anti-seizure drugs) can cause hypocalcemia. Additionally, medicines that fight bone cancers and other bone issues are also linked to the condition. These drugs include alendronate, ibandronate, risedronate, and zoledronic acid.

Alkalosis. When you have too much base (or alkali) in your body (the opposite of too much acid), your blood calcium levels can drop. Alkalosis can happen when you're vomiting or dehydrated, when you breathe too rapidly and shallowly (hyperventilation), or have certain chronic conditions.

Large blood transfusions. Calcium in your bloodstream can bind with calcium citrate, which is used to clot donated blood. That could lower your blood calcium levels.

Pregnancy. Poor diet, frequent vomiting, or other problems during pregnancy may lead to low blood calcium levels.

Cancer. Prostate cancer that spreads to the bones can cause bones to take up extra calcium, lowering blood levels. This is sometimes called "hungry bone syndrome," a term also used in some cases where the cause is low parathyroid hormone levels.

Severe infection. Any infection that triggers a dangerous inflammatory response, called sepsis, could lead to hypocalcemia. Severe Covid-19 infections have been linked to hypocalcemia as well.

You might not have any symptoms of hypocalcemia. Or you could be very sick. In some cases, the condition can be life-threatening.

Symptoms of mild hypocalcemia can include:

  • Muscle cramps in the back and legs
  • Dry, scaly skin
  • Rougher than usual hair texture
  • Brittle nails

Left untreated, hypocalcemia can affect your nervous system and your mental state. You might have symptoms such as:

  • Memory loss
  • Depression
  • Anxiety
  • Irritability
  • Hallucinations (hearing or seeing things that aren't there)

In more severe cases, symptoms can include:

  • Tingling in your lips, tongue, fingers, or feet
  • Painful muscle spasms
  • Breathing problems caused by muscle spasms in your throat
  • Seizures
  • Abnormal heartbeats (arrhythmia)
  • Heart failure

Tetany

If your doctor says you have tetany, that means you have a cluster of symptoms that can be caused by imbalances in your electrolytes — substances in your body that help regulate chemical reactions, fluid balance, and muscle contractions. Hypocalcemia is the most common cause of tetany. When your hypocalcemia symptoms involve involuntary muscle contractions and irritable nerves, you have tetany. Those symptoms include:

  • Muscle spasms
  • Burning or tingling hands and feet
  • Numbness around your mouth
  • Trouble breathing
  • Vomiting
  • Seizures

Tetany usually isn't life-threatening. But one potential complication of tetany is rhabdomyolysis, a dangerous condition in which your muscles break down. Because it can cause kidney failure and other serious problems, rhabdomyolysis is potentially fatal.

Symptoms of acute hypocalcemia

You can develop symptoms of hypocalcemia slowly or suddenly. When it happens suddenly, it's called acute hypocalcemia. When you have acute hypocalcemia, you are more likely to have symptoms associated with tetany, such as painful muscle spasms, along with breathing and heart problems, seizures, and mental changes.

You can find out if you have hypocalcemia by taking a blood test. You might get tested because of possible symptoms of hypocalcemia or because you've had a thyroid or parathyroid surgery that might affect your calcium levels. Sometimes, you find out when your doctor tests your blood for some other reason.

You might get two kinds of calcium blood tests: one for the total concentration of calcium in your blood and one for what doctors call ionized calcium. That's calcium floating free, rather than attached to certain proteins in your blood.

Your doctor also may check for two possible signs of hypocalcemia:

Chvostek sign. This is an involuntary facial twitch that happens when a nerve along your jaw is tapped. It's most common in people with acute hypocalcemia.

Trousseau sign. This is a muscle spasm in the hand and wrist that happens when a blood pressure cuff or tourniquet is tightly wrapped around your forearm for 3 minutes, reducing blood supply. The Trousseau sign is a strong indicator of hypocalcemia, showing up in more than 90% of people with hypocalcemia and rarely in those without it.

Because hypocalcemia can have many different causes, you'll likely need more tests to find out what's behind your low calcium levels and how your body is reacting. Before deciding which tests to do, your doctor will ask about your medical and family history.

Other tests might include:

  • Blood tests for levels of magnesium, phosphorus, parathyroid hormone, and vitamin D
  • Urine tests for phosphate, calcium, magnesium, and creatinine (a measure of your kidney health) 
  • Ultrasound imaging of your kidneys to look for kidney stones (seen in some people with a genetic form of hypocalcemia)
  • Genetic testing to look for inherited forms of hypocalcemia
  • Bone scans to see if you have problems, such as rickets, typically caused by low vitamin D levels

Hypocalcemia EKG

Because hypocalcemia can cause problems with your heart, you might get an electrocardiogram (EKG). This test can detect abnormal heart rhythms, which can happen with hypocalcemia.

For the test, you'll get sensors stuck on your chest, legs, and arms that send electrical signals to a computer. The computer will create a chart that shows your heart rhythms.

How do you fix hypocalcemia? The treatment you get will depend on the cause and how severe your symptoms are.

The most common treatments fall into these categories:

Calcium pills. If your symptoms are mild, you might be able to restore your calcium levels with daily supplements. A typical amount would be 1,500 to 2,000 milligrams, divided into two or three daily doses -- which is more than the amount recommended for healthy people just trying to maintain normal calcium levels. You might take vitamin D along with the calcium, to aid absorption, especially if your vitamin D levels also are low.

Intravenous calcium. If you have severe symptoms, heart rhythm disturbances, or the sudden onset of hypocalcemia, you're likely to be hospitalized so you can get calcium directly in your veins through an IV line, a tube usually put in your arm or hand. You might get a form called calcium gluconate or, less commonly, a form called calcium chloride. After IV treatment, you can expect to take supplements for a while as well.

Recombinant human parathyroid hormone. When low calcium is caused by low levels of PTH, you might get a manufactured form of the hormone, given as injections. However, its use is limited due to factors such as cost, availability, and concerns about long-term side effects, such as bone pain. But additional versions are under study.

You might also get treatments to address underlying causes and particular symptoms, such as:

  • Magnesium supplements or IV treatments if your levels are low
  • High doses of vitamin D if your levels are very low
  • Changes in your diet and fluid intake if you've had kidney stones
  • Thiazide diuretics (medicines that can lower the amount of calcium you lose in your pee)

Tetany treatment

When you have tetany caused by hypocalcemia, the first aim of treatment is to restore normal calcium levels — which often means IV treatment with calcium gluconate. You might have a quick change in your symptoms, but the improvement might not last very long. Sometimes, you might need a few more doses over 12-24 hours.‌

Some milder cases can be treated with calcium supplements. You might take magnesium and vitamin D pills as well.

Hypocalcemia symptoms usually go away when you get treatment and your blood calcium levels get back to normal. But untreated hypocalcemia can cause complications such as:

  • Heart failure
  • Seizures
  • Life-threatening heart rhythm disturbances

In some cases of chronic hypocalcemia, you might have to take high doses of calcium and vitamin D for a long time, which can cause side effects, such as kidney stones.

If you have persistently low levels of parathyroid hormone (which is a common cause of low calcium levels), you also face an increased risk of kidney stones and chronic kidney disease.

When you have hypocalcemia, or low blood calcium levels, it's important to get treatment to clear up your symptoms and avoid potentially serious complications. It's also important to find out what caused your low calcium levels so you can get any additional treatment you need. You may need treatment for a short or long time, depending on the cause.