Severe low calcium (hypocalcaemia): a case-based approach

The presentation

Imagine an adult who has recently had thyroid surgery. Over a day or two they notice tingling and numbness around the mouth and in the fingers and toes, then painful cramps and twitching in the hands and feet. The muscles of the hands may draw into a stiff, claw-like spasm. They may feel anxious, jittery or confused, and in severe cases can have a fit or an abnormal heart rhythm. This over-excitable, twitchy pattern — pins and needles around the mouth and fingertips, cramping spasms, and muscle twitches — is the hallmark of low blood calcium. It is quite different from ordinary tiredness or a simple cramp after exercise, and when it appears in someone at risk, such as after neck surgery, it should be taken seriously and checked urgently.

Why low calcium causes these symptoms

Calcium does far more than build bones. It helps control how nerves send signals and how muscles contract and relax. When the blood calcium level drops too low, nerves and muscles become unstable and fire too easily, so the body becomes over-excitable — hence the tingling, twitching and spasms. If the level falls far enough, this instability can affect the muscles of breathing, cause generalised fits, or disturb the heart's electrical rhythm, which is what makes severe hypocalcaemia potentially dangerous. The body normally keeps calcium in a tight range using hormones and vitamin D, so a very low level usually means something has upset that control — for example, damage to the small glands in the neck that regulate calcium, or a severe lack of vitamin D. Treatment aims to restore calcium safely and correct the underlying cause.

When to call 999

Call 999 or go straight to A&E if someone has severe symptoms of low calcium: a fit or seizure, difficulty breathing, tightness or spasm of the throat, severe or spreading muscle spasms, a fast, slow or irregular heartbeat, fainting, or becoming confused or unresponsive. These may mean the calcium level is dangerously low and needs urgent treatment in hospital. Milder symptoms — mild tingling around the mouth or fingertips, or occasional cramps — in someone known to be at risk still need prompt medical advice the same day, so contact NHS 111 or your doctor. Do not try to treat severe symptoms with extra supplements at home, as the level needs checking and correcting under medical supervision. While waiting for help, keep the person calm and note when the symptoms started and how they are changing.

Who is more at risk

Several situations make low calcium more likely. A common cause is a problem with the parathyroid glands — four tiny glands in the neck that control calcium — which can be damaged or removed during thyroid or neck surgery, causing calcium to fall in the days afterwards. A severe lack of vitamin D, which helps the gut absorb calcium, is another important cause, as are certain kidney problems, some medicines, and low levels of another mineral, magnesium. Being seriously unwell can also disturb calcium. People who have had neck surgery, who have known parathyroid or vitamin D problems, or who take calcium-affecting medicines should be alert to symptoms. Knowing you are at risk lowers the threshold for getting checked, because the same tingling-and-spasm pattern that might be ignored in others is an important warning sign in these groups.

The safe pathway

The practical rule is to match the response to the severity. Mild, occasional cramps in a well person are common and usually harmless. But tingling around the mouth and fingertips, cramping spasms or muscle twitching — especially in someone at risk, such as after neck surgery or with known vitamin D or parathyroid problems — should prompt prompt medical advice and a blood test to check the calcium level. Severe features — a fit, throat spasm, difficulty breathing, an irregular heartbeat, fainting or confusion — are a 999 emergency. Anyone on calcium or vitamin D treatment should take it exactly as prescribed and attend blood tests to keep the level in the safe range, since both too little and too much calcium cause problems. Severe hypocalcaemia is uncommon, but recognising the pattern and getting the level checked prevents it becoming dangerous.