Why does leukaemia cause unexplained fever?

Leukaemia can cause unexplained fever because abnormal blood cells disrupt normal immune defences, while inflammation or an infection can raise body temperature. Unexplained Fever is a very common presentation of Leukaemia. The fever may come and go, and an obvious source such as a cough or urinary symptom may not be present at first.

Leukaemia affects the bone marrow, where blood cells are made. Although the blood may contain many abnormal white cells, they may not protect the body effectively. At the same time, the marrow may make fewer working infection-fighting cells. This can allow an infection to develop quickly or make its signs less typical.

Fever can also reflect the immune system releasing inflammatory chemicals in response to the disease. Medicines, transfusions, or other treatment can sometimes contribute as well. A fever does not identify its cause by itself, so clinicians may check the temperature, examine you, and arrange blood or other tests.

If leukaemia is known or suspected, contact the treating haematology team promptly about a new or persistent fever and follow their temperature instructions. Record when the fever began, the readings, chills or sweats, and any symptoms such as cough, sore throat, diarrhoea, pain when passing urine, or a new rash. Do not start leftover antibiotics or assume that the absence of local symptoms rules out infection.

Drink fluids if you can do so safely, rest, and use only fever medicine that your clinical team has approved. Some medicines can hide a rising temperature or affect bleeding risk, which may matter when blood counts are abnormal.

Seek urgent medical advice for a high or rising temperature, shaking chills, confusion, unusual sleepiness, trouble breathing, chest pain, severe weakness, or inability to keep fluids down. Seek immediate help for signs of sepsis, such as rapidly worsening illness, faintness, cold or clammy skin, or new difficulty staying awake. If you are receiving leukaemia treatment, use the emergency number given by your team rather than waiting for the next appointment.

Ask which temperature reading should trigger a call, whether you should go directly to an emergency department, and which medicines are safe for you. You can also ask what your recent blood counts mean, how infection will be assessed, and whether a treatment or transfusion could be contributing to the fever.