Hypocalcaemia / Low Calcium 

What is hypocalcaemia?

Hypocalcaemia is a medical condition in which the level of calcium in the blood falls below the normal range. Calcium is essential for many vital functions, including building strong bones and teeth, enabling muscle contraction, transmitting nerve signals and maintaining a regular heartbeat.

Normally, calcium levels are tightly regulated by the parathyroid glands, kidneys, intestines and vitamin D. When this balance is disrupted, due to underactive parathyroid glands, kidney problems, severe vitamin D deficiency, or other medical conditions, blood calcium levels drop, leading to hypocalcaemia.

The severity of hypocalcaemia can vary. Mild cases may cause no symptoms, while more significant calcium deficiency can result in muscle cramps, tingling, fatigue, seizures or dangerous disturbances in heart rhythm. Because of its impact on multiple organs, hypocalcaemia requires prompt medical evaluation and treatment.

Why is hypocalcaemia a hormone-related problem?

Hypocalcaemia is closely linked to hormonal regulation because calcium balance in the body is largely controlled by the endocrine system. The parathyroid glands secrete parathyroid hormone (PTH), which raises blood calcium by stimulating calcium release from bone, increasing kidney calcium reabsorption and activating vitamin D. Vitamin D (calcitriol), in turn, enhances calcium absorption from the gut, while calcitonin has a minor role in lowering calcium by inhibiting bone resorption.

When these regulatory pathways are impaired (for example, reduced PTH secretion in hypoparathyroidism, resistance to PTH in pseudohypoparathyroidism, or inadequate vitamin D activation in chronic kidney disease) calcium cannot be properly absorbed, mobilised, or retained. This disruption of hormonal control directly leads to persistently low calcium levels in the blood, making hypocalcaemia fundamentally a hormone-related problem.

What causes hypocalcaemia?

Hypocalcaemia develops when the body cannot maintain normal calcium balance. This may be due to problems with calcium regulation, poor absorption or excessive losses in urine. Common causes include:

• Hypoparathyroidism — underactive or damaged parathyroid glands (often after thyroid or neck surgery or irradiation) reduce parathyroid hormone (PTH), which is essential for keeping calcium levels normal.

• Vitamin D deficiency — vitamin D is needed for calcium absorption from food. Low levels, often due to lack of sunlight, poor diet or certain medical conditions, can lead to hypocalcaemia.

• Kidney disease — chronic kidney disease impairs the kidneys’ ability to convert vitamin D into its active form and to regulate calcium and phosphate balance.

• Magnesium deficiency — low magnesium can interfere with PTH secretion and function, indirectly lowering calcium levels.

• Medications — some drugs, such as bisphosphonates, chemotherapy agents or certain anticonvulsants, may cause low calcium.

• Genetic conditions — rare inherited disorders can affect how calcium is regulated in the body.

• Severe illness or pancreatitis — acute medical conditions may cause sudden drops in calcium due to shifts in body chemistry.

Identifying the underlying cause is essential, as treatment focuses on correcting both the low calcium and its root trigger.

What are the symptoms of hypocalcaemia?

The symptoms of hypocalcaemia depend on how low the calcium levels are and how quickly they drop. Some people with mild cases may have no obvious signs, while others may develop more serious problems affecting the nerves, muscles, heart and brain.

• Mild hypocalcaemia — may cause no noticeable symptoms, or only subtle issues such as fatigue, irritability or mild muscle cramps.

• Moderate hypocalcaemia — symptoms become more apparent and can include:
  • Tingling or numbness around the lips, fingers and toes
  • Muscle cramps or spasms
  • Twitching of facial muscles (known as Chvostek’s sign)
  • Difficulty concentrating or feeling unusually anxious

• Severe hypocalcaemia — very low calcium levels can be dangerous, leading to:
  • Painful muscle contractions (tetany) affecting the hands, feet or face
  • Seizures
  • Irregular heart rhythm (arrhythmia)
  • Low blood pressure
  • Confusion or loss of consciousness

Because symptoms can overlap with other conditions, blood tests are essential for confirming hypocalcaemia and guiding treatment.

What is the difference between hypocalcaemia and hypercalcaemia?

Hypocalcaemia occurs when calcium levels in the blood fall below normal, most often due to underactive parathyroid glands, vitamin D deficiency, chronic kidney disease or magnesium deficiency. It commonly affects the nerves and muscles, causing tingling around the lips and fingers, painful cramps or spasms, seizures and in severe cases, dangerous disturbances in heart rhythm. 

By contrast, hypercalcaemia is the state of having abnormally high calcium levels in the blood, usually linked to overactive parathyroid glands, certain cancers or excessive vitamin D or calcium intake. It may cause thirst, frequent urination, constipation, abdominal discomfort, confusion and irregular heartbeat, with long-term risks such as kidney stones and bone loss.

What are the complications of untreated hypocalcaemia?

If hypocalcaemia is not recognised and treated, persistently low calcium levels can lead to serious and sometimes life-threatening complications:

• Neuromuscular problems — prolonged low calcium can cause chronic muscle cramps, painful spasms (tetany), seizures and abnormal reflexes, which may interfere with daily life.

• Heart complications — severe hypocalcaemia can disrupt the heart’s electrical activity, leading to arrhythmias, heart failure or even cardiac arrest.

• Bone health issues — long-term calcium deficiency may contribute to weak or brittle bones, increasing the risk of osteoporosis and fractures.

• Dental problems — in children, untreated hypocalcaemia can affect tooth development, while in adults it may lead to enamel defects and gum disease.

• Cataracts and eye problems — chronic low calcium may cause deposits in the eye lens, leading to cataracts and vision impairment.

Because calcium plays a role in so many body systems, hypocalcaemia should never be ignored. Early diagnosis and management can prevent long-term damage and restore normal function.

Who is at risk of hypocalcaemia in Singapore? 

Hypocalcaemia can affect people of all ages, but some groups are more likely to develop it:

• People with parathyroid disorders — those with underactive or surgically removed parathyroid glands (hypoparathyroidism) are at high risk. Dr Dinesh says this is the most common cause, often due to damage during removal of the thyroid gland or tumors of the neck. 

• Patients with chronic kidney disease — kidney problems reduce vitamin D activation and disturb calcium balance, making low calcium more likely.

• Individuals with vitamin D deficiency — people with little sun exposure, poor nutrition or malabsorption conditions such as coeliac or Crohn’s disease are at increased risk.

• Those with magnesium deficiency — low magnesium can interfere with calcium regulation, predisposing to hypocalcaemia. Dr Dinesh comments that anti-acid medication is a common cause of this. 

• People on certain medications — drugs such as bisphosphonates, chemotherapy agents or long-term anticonvulsants can lower calcium levels.

• Infants and children — especially premature babies or those born to mothers with poorly controlled diabetes, as their calcium regulation may be immature.

• Older adults — reduced dietary intake, less efficient vitamin D absorption and chronic illness all contribute to higher risk.

Recognising who is at risk helps ensure early testing and timely treatment, reducing the chance of serious complications.

How is hypocalcaemia diagnosed?

Diagnosis of hypocalcaemia involves confirming low calcium levels in the blood and identifying the underlying cause. Doctors usually use a combination of medical history, examination and tests.

• Blood tests — a standard blood test checks total and ionised calcium levels. Additional tests may include parathyroid hormone (PTH), vitamin D, magnesium, phosphate and kidney function to pinpoint the cause.

• Urine tests — a 24-hour urine collection may be used to see how much calcium is being lost through the kidneys.

• Electrocardiogram (ECG) — low calcium can affect the heart’s rhythm. An ECG may be performed to detect changes such as a prolonged QT interval.

• Medical history and examination — your doctor will review your symptoms, medications, family history and any conditions that could interfere with calcium regulation.

Accurate diagnosis is essential, as treatment must address both the low calcium and the condition causing it.

What are the treatment options for hypocalcaemia in Singapore? 

Treatment for hypocalcaemia depends on how low the calcium level is, the severity of symptoms and the underlying cause. The goal is to restore normal calcium levels and prevent complications.

• Calcium supplementation — mild cases may be managed with oral calcium tablets, while severe cases often require intravenous (IV) calcium for rapid correction, especially if there are muscle spasms, seizures or heart rhythm disturbances.

• Vitamin D therapy — vitamin D (or its active forms such as calcitriol) is prescribed to improve calcium absorption from the gut, particularly in people with vitamin D deficiency or chronic kidney disease.

• Magnesium replacement — if hypocalcaemia is caused or worsened by magnesium deficiency, correcting magnesium levels is essential for calcium balance to improve. For some, we have to stop a medication called Proton Pump Inhibitors which lower magnesium (used for gastritis). 

• Treating underlying conditions — managing the root cause is crucial. For example, patients with hypoparathyroidism may need long-term calcium and activated vitamin D (Calcitriol), while those with kidney disease may require specialised treatments to control calcium and phosphate levels.

With proper treatment, calcium levels can usually be stabilised and most patients recover well. Ongoing monitoring is often needed, especially for people with chronic conditions.

Prognosis and Recovery

The outcome of hypocalcaemia varies depending on its cause, severity and how quickly it is treated. With proper management, most people recover well and avoid serious complications.

• Short-term causes — hypocalcaemia due to vitamin D deficiency, poor nutrition or medication side effects usually improves once the underlying issue is corrected.

• Chronic conditions — patients with hypoparathyroidism or chronic kidney disease may need lifelong treatment with calcium and vitamin D, along with regular monitoring.

• Long-term outlook — with consistent care, most people can live normal, healthy lives, although some may experience recurring symptoms if calcium levels are not well controlled.

• Severe untreated cases — without treatment, hypocalcaemia can cause seizures, heart rhythm disturbances or breathing difficulties, which may be life-threatening.

Overall, early diagnosis and ongoing management give most patients an excellent chance of recovery and long-term stability.

Summary 

Hypocalcaemia, or low calcium in the blood, can range from mild and temporary to severe and life-threatening. It may result from vitamin D deficiency, kidney disease, parathyroid disorders or other underlying conditions. Symptoms often involve the nerves and muscles, such as tingling, cramps or spasms, but in severe cases can progress to seizures, breathing difficulties or abnormal heart rhythms.

If you are experiencing symptoms suggestive of low calcium, schedule a consultation with us at The Metabolic Clinic for detailed evaluation, tailored treatment and ongoing care to restore balance and protect your long-term health.

Frequently Asked Questions (FAQs)