What are the risk factors for high calcium in cancer?

Hypercalcaemia means that the calcium level in the blood is higher than the body can safely regulate. Cancer can cause this when cells in or near bone increase bone breakdown. Some tumours release hormone-like signals that make the kidneys retain calcium and make bones release more of it. Multiple myeloma can damage areas of bone and contribute to this process.

The symptoms may be subtle at first. Thirst, passing urine often, constipation, nausea, poor appetite, tiredness, muscle weakness, confusion or new drowsiness can occur. These symptoms are not specific to high calcium, so a blood test is needed rather than relying on how you feel.

Tell your oncology team about new thirst, constipation, vomiting, reduced alertness or worsening weakness. They may review medicines, hydration, kidney function and blood calcium, alongside the cancer itself. Drink according to the advice of your clinical team, particularly if you have kidney, heart or fluid-balance problems. Do not take calcium or vitamin D supplements for this concern without checking first.

Seek urgent medical help for confusion, severe drowsiness, repeated vomiting, inability to keep fluids down, fainting, marked weakness or a major change in urine output. A person who is difficult to wake or cannot drink safely needs emergency assessment. Prompt treatment can address dehydration and the underlying calcium disturbance while the cancer team investigates its cause.

Could my symptoms be related to high calcium? When should my calcium and kidney function be checked? Are any of my medicines or supplements contributing? Is there evidence of bone involvement or multiple myeloma? What warning signs should lead me to contact the hospital?