Low haemoglobin can develop in people with cancer because of the disease itself, blood loss or treatments such as chemotherapy and radiotherapy. The condition, known as anaemia, can cause fatigue, dizziness, breathlessness and a rapid heartbeat, although some people have few or no symptoms.
Anaemia can affect a patient’s ability to tolerate cancer treatment, but its severity and the appropriate response depend on the underlying cause, the person’s symptoms and their overall health.
How cancer can cause anaemia
Haemoglobin is a protein in red blood cells that carries oxygen from the lungs to tissues throughout the body. When haemoglobin levels fall below the normal range, the body may receive less oxygen than it needs, leading to symptoms such as weakness and shortness of breath.
Cancer can contribute to anaemia in several ways. Leukaemia, lymphoma and multiple myeloma can affect the bone marrow, the tissue inside bones responsible for producing blood cells. When the marrow cannot make enough healthy red blood cells, haemoglobin levels may fall.
Other cancers can cause anaemia through bleeding, inflammation or damage to organs involved in blood production. Tumours in the digestive tract, for example, may cause blood loss that reduces the body’s iron stores.
Cancer treatments can also contribute. Chemotherapy and radiotherapy may affect the production of blood cells, while some patients develop anaemia because of poor nutrition, iron deficiency or other illnesses.
Low haemoglobin does not automatically mean a person has cancer. Iron deficiency, vitamin B12 or folate deficiency, chronic kidney disease, infections and other conditions can also cause anaemia.
Symptoms of low haemoglobin
The symptoms depend on how low the haemoglobin level has fallen and how quickly it has declined. Some people develop symptoms gradually, while others may notice changes over a shorter period.
Common signs include:
- Persistent tiredness or weakness.
- Shortness of breath, particularly during physical activity.
- Dizziness or light-headedness.
- A rapid or noticeable heartbeat.
- Headaches.
- Pale skin or pale nail beds.
More severe anaemia can put additional strain on the heart and other organs. Chest pain, breathlessness at rest, fainting or a markedly irregular heartbeat require urgent medical assessment.
These symptoms are not specific to cancer. Their presence alone cannot establish whether someone has cancer or determine which condition is responsible.
How doctors diagnose anaemia
Doctors usually begin with a complete blood count, a blood test that measures haemoglobin and other blood components. The results help establish whether anaemia is present and how severe it may be.
Further investigations depend on the findings and the patient’s medical history. They may include tests for iron, vitamin B12 and folate levels, kidney function and signs of blood loss.
If a doctor suspects that the bone marrow is affected, additional investigations may be necessary. These can include a bone marrow biopsy, in which a sample of marrow is collected for examination. The procedure is not required for every person with low haemoglobin.
A haemoglobin level below 8 grams per decilitre is not a universal definition of anaemia. Anaemia is identified using thresholds that vary according to factors including age, sex and pregnancy status. The severity of the condition and the need for treatment must also be assessed in the patient’s clinical context.
Treatment options for cancer-related anaemia
Treatment depends on what is causing the low haemoglobin, how severe the anaemia is and whether the patient is receiving cancer treatment.
Iron replacement: Iron supplements, taken orally or given intravenously, may be prescribed when tests confirm iron deficiency. Vitamin B12 or folate supplements may be appropriate when a deficiency in either nutrient is responsible.
Eating iron-rich foods, including beans, dark green leafy vegetables, meat and iron-fortified cereals, can support nutritional needs. However, diet alone may not correct significant anaemia, particularly when cancer, ongoing bleeding or treatment-related effects are involved. Iron supplements should not be taken automatically without establishing whether iron deficiency is present.
Blood transfusions: A red blood cell transfusion can raise haemoglobin more quickly and may be considered when levels are very low, symptoms are significant or there is active bleeding. The decision depends on the patient’s condition rather than a single laboratory result.
Medicines that stimulate red blood cell production: Erythropoiesis-stimulating agents (ESAs) encourage the bone marrow to produce more red blood cells. Their use in cancer care is restricted because they can increase the risk of blood clots and may carry other risks in certain cancer settings.
The American Society of Clinical Oncology and the American Society of Hematology recommend that these medicines may be considered for selected patients whose anaemia is associated with chemotherapy and whose cancer treatment is not intended to cure the disease. They generally should not be used for chemotherapy-related anaemia when treatment is intended to cure cancer. Decisions require an individual assessment of potential benefits and risks.
Doctors may also need to address the underlying cause, investigate bleeding or review the cancer treatment contributing to the anaemia.
When to seek medical attention
People undergoing cancer treatment should report persistent fatigue, dizziness, breathlessness or a racing heartbeat to their healthcare team. Regular blood tests can help clinicians identify falling haemoglobin levels and determine whether treatment is needed.
Anyone experiencing chest pain, severe breathlessness at rest, fainting or uncontrolled bleeding should seek emergency medical care.
The central consideration is identifying why haemoglobin is low. Treating iron deficiency, managing treatment-related effects and addressing the underlying disease require different approaches, so care should be guided by clinical assessment and blood test results.
