Confusion, thirst and drowsiness: recognising high calcium

High calcium in the blood, called hypercalcaemia, is one of the more common emergencies in advanced cancer. In breast cancer it most often happens when cancer has spread to the bones, causing bone to break down and release calcium into the bloodstream. Sometimes cancer cells also release a hormone-like substance that raises calcium even without much bone spread. When calcium rises, it affects the brain, kidneys, bowel and heart. Early symptoms can be vague and easy to mistake for side effects of treatment or simple tiredness: feeling very thirsty, passing large amounts of urine, loss of appetite, feeling sick or vomiting, constipation, tummy pain, muscle weakness, and feeling unusually tired or low. As calcium climbs higher, people may become drowsy, confused, muddled or agitated, and family often notice the change first. Very high calcium can cause dehydration, kidney problems, abnormal heart rhythms and, rarely, coma. High calcium is diagnosed with a simple blood test and is usually very treatable with fluids through a drip and medicines that slow bone breakdown. Because symptoms can worsen quickly, anyone with breast cancer and these symptoms should seek same-day medical advice.

Who is at higher risk

People with bone metastases, widespread disease, dehydration, kidney problems, or those taking certain medicines that raise calcium are at higher risk.

How it is diagnosed

A blood test measures calcium, usually adjusted for the level of albumin, a blood protein. Kidney function, and sometimes a heart tracing, are also checked.

Family can help spot it

Relatives who notice new confusion, sleepiness or unusual thirst should contact the care team promptly.

High calcium is serious, but it usually responds well to prompt treatment. It is also a sign that the cancer may be active, which your team will consider.

Most people improve within days

Confusion, thirst and sickness usually ease as calcium falls over a few days of treatment.

It can come back

Unless the cancer is controlled, calcium may rise again, so blood tests are repeated and bone medicines may be continued.

It may prompt a treatment review

High calcium can suggest the cancer is progressing, so scans or changes to cancer treatment may be discussed.

Kidneys need protection

Dehydration and some treatments affect the kidneys, so kidney tests guide medicine doses.

What this page cannot tell you

It cannot interpret your blood results. Ask your team what your calcium level means.

You cannot always prevent high calcium, but some steps help.

Stay well hydrated

Drink enough fluids through the day, especially in hot weather or when vomiting or having loose motions, unless your team has advised a fluid limit.

Continue bone medicines

Regular bone-strengthening medicines for bone metastases lower the risk of high calcium and fractures.

Check supplements

Ask your team before taking calcium or vitamin D supplements if you have bone metastases.

Keep up blood tests

Regular calcium checks catch rises early.

Keep moving

Long periods in bed increase bone breakdown. Gentle movement, if safe, helps.

Once calcium has come down and you are home, a few steps help you recover and lower the chance of another episode going unnoticed.

Follow-up blood tests

Calcium and kidney function are usually rechecked within one to two weeks, and then at regular intervals. Keep these appointments even if you feel well.

Drink steadily

Sip fluids through the day. Water, buttermilk, coconut water and soups can help, unless your team has advised limits because of heart or kidney problems.

Review your medicines

Your team may stop calcium or vitamin D tablets, change water tablets or adjust other medicines. Keep an updated list and share it at every visit.

Know the early signs

Write down the symptoms you had this time, such as thirst, sickness or muddled thinking, so you and your family can spot them early if they return.

Plan for cancer treatment

Your oncologist will discuss whether cancer treatment needs to change, as controlling the cancer is the best way to keep calcium stable.