Why does acute lymphoblastic leukaemia cause unexplained fever?

Unexplained Fever is a very common presentation of Acute Lymphoblastic Leukaemia. Fever may be the result of the leukaemia itself, an infection that the immune system is less able to control, or both at the same time.

Acute lymphoblastic leukaemia starts in blood-forming tissue, where abnormal lymphoblasts multiply. As these cells take up space in the marrow, production of normal white blood cells can fall. Some white blood cells help recognise and control infection, so a person may develop fever even when there is no obvious cough, wound or urinary symptom.

Leukaemia cells and the immune response can also release chemical signals that affect the brain's temperature-control centre. This can produce fever, chills, sweating or a feeling of being unwell. Fever can come and go, and its pattern does not identify the cause by itself. A clinician may need an examination and blood tests to separate infection from inflammation or treatment-related effects.

If acute lymphoblastic leukaemia is known or suspected, contact the oncology team promptly when a fever appears. Follow the team’s instructions about checking your temperature, taking medicines and attending assessment. Do not start leftover antibiotics or assume that the absence of another symptom makes the fever harmless.

Keep a note of when the fever began, how it changes, and any chills, rash, mouth soreness, cough, breathlessness, pain or change in alertness. Tell the clinician about recent treatment, medicines, sick contacts and any device such as a central line. These details help guide examination and testing.

Seek urgent medical advice for a new or persistent fever during leukaemia evaluation or treatment, especially with shaking chills, confusion, marked weakness, breathing difficulty, chest pain, severe pain, repeated vomiting, or a rapidly worsening condition. A weakened immune defence can allow an infection to progress quickly, and early assessment matters even when the source is not obvious.

Call emergency services for severe breathing problems, collapse, new confusion or difficulty staying awake. Use the emergency pathway provided by your oncology team, and tell staff that acute lymphoblastic leukaemia is present or being investigated.

Ask what temperature threshold and contact number your care team uses, whether you should take a fever-reducing medicine before assessment, and which symptoms should prompt emergency care. You can also ask how blood counts, cultures and other tests will help distinguish infection from leukaemia-related inflammation.