Chronic Myeloid Leukemia (CML) is a type of blood cancer that originates in the bone marrow and leads to uncontrolled growth of white blood cells. Diagnosing CML requires a combination of blood tests, bone marrow examination, and genetic testing to confirm the presence of specific abnormalities.
Here’s a breakdown of the key diagnostic criteria used by doctors.
1. Complete Blood Count (CBC) with Differential
A CBC test is usually the first step in diagnosing CML. It often shows:
- Increased white blood cell (WBC) count (often above 100,000 cells per microliter).
- Elevated platelets (thrombocytosis) in some cases.
- Low red blood cell (RBC) count, leading to anemia.
- Presence of immature white blood cells (blasts, myelocytes, and promyelocytes) in circulation.
2. Peripheral Blood Smear
A microscopic examination of the blood confirms:
- A mix of mature and immature granulocytes (a type of white blood cell).
- A high number of basophils and eosinophils, which are usually uncommon in healthy blood.
3. Bone Marrow Aspiration and Biopsy
A sample of bone marrow (from the hip bone) is analyzed for:
- Hypercellularity (increased blood-forming cells).
- Increased granulocytes and megakaryocytes (platelet-producing cells).
- A low percentage of blasts in the chronic phase.
4. Genetic Testing: The Philadelphia Chromosome (Ph1) and BCR-ABL1 Fusion Gene
The most defining characteristic of CML is the presence of the Philadelphia chromosome, which results from a swap of genetic material between chromosomes 9 and 22. This creates the BCR-ABL1 fusion gene, which produces an abnormal protein that drives uncontrolled cell growth.
Testing methods include:
✅ Fluorescence in situ hybridization (FISH) – Detects the Philadelphia chromosome.
✅ Polymerase chain reaction (PCR) – Identifies and measures the BCR-ABL1 fusion gene, even in small amounts.
✅ Karyotyping – Analyzes chromosomes for the translocation between 9 and 22.
5. Staging CML: Phases of the Disease
CML is categorized into three phases based on blast cell percentage in the blood or bone marrow:
- Chronic Phase (≤10% blasts) – Most patients are diagnosed in this phase. Symptoms are mild or absent, and treatment is most effective.
- Accelerated Phase (10-19% blasts) – Worsening symptoms, increased immature cells, and resistance to treatment may occur.
- Blast Crisis (≥20% blasts) – A critical phase where CML behaves like acute leukemia, requiring aggressive treatment.
Final Thoughts
Diagnosing CML involves a combination of blood tests, bone marrow analysis, and genetic screening. The presence of the Philadelphia chromosome and BCR-ABL1 gene is the hallmark of the disease. Early detection, especially in the chronic phase, allows for effective targeted therapy, improving patient outcomes.