How leukemia differs from other illnesses
Tiredness, fever, bruising and swollen lymph nodes occur in many illnesses. This topic covers the main conditions that can look like leukemia and how doctors tell them apart.
01Short answer
02Simple explanation
Anemia is most often due to low iron, B12 or folate. Usually only the red cells change, while white cells and platelets stay normal.
Viral infections, especially glandular fever (infectious mononucleosis), can cause fever, sore throat, swollen nodes and altered lymphocytes. But these changes settle within a few weeks.
Immune thrombocytopenia (ITP) causes bruising and petechiae, but the other blood cells are usually normal.
In leukemia, several cell lines often change together and immature cells (blasts) appear on the smear.
03Scientific explanation
Blood count and smear: according to MedlinePlus and the ACS, the first step is a full blood count and a smear under the microscope. A fall in two or three cell lines together (pancytopenia) or many blasts make leukemia more likely, but pancytopenia also occurs in aplastic anemia, B12 deficiency and severe infections.
Leukemoid reaction: in severe infection or inflammation, white cells can rise very high. The cells are mostly mature, and counts return to normal once the cause is treated.
Related diseases: according to the LLS, myelodysplastic syndromes (MDS) and myeloproliferative neoplasms are also bone marrow diseases and can resemble leukemia. They are distinguished by the percentage of blasts in the marrow and by genetic changes.
04What happens in the body?
How does a doctor tell the difference?
First a detailed history and examination: when symptoms began, recent infections, medicines. Then a full blood count. The test may be repeated, because counts can return to normal a few weeks after an infection. If doubt remains, a bone marrow test is done.
Conditions that closely resemble leukemia
Glandular fever, severe bacterial infections, iron and B12 deficiency, immune thrombocytopenia, aplastic anemia, side effects of some medicines, lymphomas and myelodysplastic syndromes. Many are told apart with simple tests.
Why not draw your own conclusions?
Reading symptom lists online often causes needless fear or, the opposite, lost time. One blood test gives a more accurate answer than hours of searching.
05From similar symptoms to a clear answer
How a doctor reasons (simplified).
06Conditions that resemble leukemia
| Condition | Shared sign | Difference on tests |
|---|---|---|
| Iron-deficiency anemia | Tiredness, paleness | Only red cells small and low; low ferritin |
| Glandular fever | Fever, throat, nodes | Atypical lymphocytes, positive virus test |
| Immune thrombocytopenia | Bruising, petechiae | Only platelets low |
| B12 deficiency | Tiredness, sometimes pancytopenia | Large red cells, low B12 |
| Myelodysplastic syndrome | Anemia, infections | Marrow blasts under 20%, dysplasia |
* The final decision is made by a hematologist.
07Key terms
- Pancytopenia
- A fall in all three blood cell lines.
- Blood smear
- Looking at blood on a glass slide under a microscope.
- Leukemoid reaction
- A very high white count caused by infection or inflammation.
- MDS
- A disease in which the marrow makes faulty blood cells.
- Ferritin
- A protein that reflects the body’s iron stores.
08Key points
- Symptoms are not specific to leukemia.
- A blood count and smear show the difference.
- Changes in several cell lines together need attention.
- Changes after an infection settle within weeks.
- The final diagnosis is made from the bone marrow.
- Do not diagnose yourself.
09Frequently asked questions
Can glandular fever look like leukemia on tests?
Yes, altered lymphocytes can appear. But a specific virus test is positive and counts return to normal within a few weeks.
My white count is high. Is it leukemia?
Usually not: infections, stress, smoking and some medicines raise white cells. Your doctor will look at a smear and a repeat test.
Why does my doctor repeat the test?
To separate temporary changes from lasting ones. This is a normal and sound approach.
Is MDS leukemia?
MDS is a separate disease, but in some cases it can progress to AML. Your hematologist will explain this separately.
10Questions for your doctor
Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.
Can glandular fever look like leukemia on tests?
My white count is high. Is it leukemia?
Why does my doctor repeat the test?
Is MDS leukemia?
12Sources
- NHS. Acute leukaemia: Diagnosis
- American Cancer Society. Tests for Acute Myeloid Leukemia (AML)
- MedlinePlus. Complete Blood Count (CBC)
- MedlinePlus. Infectious Mononucleosis
- MedlinePlus. Iron-deficiency anemia
- Leukemia & Lymphoma Society. Myelodysplastic Syndromes
- Cancer Research UK. Getting diagnosed with acute myeloid leukaemia
- Annals of Oncology (ESMO), 2021. Chronic lymphocytic leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
- The Lancet Oncology, 2016. An international prognostic index for patients with chronic lymphocytic leukaemia (CLL-IPI): a meta-analysis of individual patient data
- American Journal of Hematology, 2025. Chronic Lymphocytic Leukemia: 2025 Update on the Epidemiology, Pathogenesis, Diagnosis, and Therapy