What Tests Confirm Philadelphia-Positive CML and Its Phase?

If you have been told you might have Philadelphia chromosome-positive chronic myeloid leukemia (Ph+ CML), your medical team will order a specific set of tests. This initial workup confirms the diagnosis, determines the phase of the disease, and helps select the safest, most effective targeted therapy (a medication called a tyrosine kinase inhibitor, or TKI) ^[1][2]. While this comprehensive testing is important, your doctor may start your treatment urgently before every single result returns, depending on your symptoms and blood counts.

Blood and Bone Marrow Tests

The foundation of a CML diagnosis involves analyzing your blood and the factory where blood cells are made: your bone marrow ^[2].

• Complete Blood Count (CBC) with Differential and Blood Smear: A routine blood draw measures your red cells, white cells, and platelets. A pathologist (a doctor who analyzes tissues) examines the blood smear under a microscope to check for high numbers of certain white blood cells (like basophils) and to count blasts (immature leukemia cells) circulating in your bloodstream ^[1][3].
• Bone Marrow Aspiration and Biopsy: Using a local anesthetic to numb your hip bone, a doctor extracts a sample of liquid marrow (aspiration) and a tiny piece of the spongy bone (biopsy). You may feel brief pressure or pain. This test allows the team to accurately count the blast cells inside the marrow and identify the disease phase ^[3].

Genetic and Molecular Testing

CML is driven by the Philadelphia chromosome—an acquired (not inherited) genetic change where two chromosomes swap DNA, creating a fusion gene called BCR::ABL1 ^[4]. The initial workup looks for this fusion gene, rather than testing for drug-resistance mutations, which are usually only checked later if a treatment stops working.

• Chromosome Analysis (Karyotype): This test examines your chromosomes’ physical appearance. It confirms the Philadelphia chromosome and checks for “additional chromosomal abnormalities” (ACAs). While some specific ACAs indicate a higher-risk disease, others do not, so your doctor will interpret exactly which ones (if any) are present ^[5][6].
• FISH (Fluorescence in situ hybridization): This sensitive test uses glowing probes to detect the BCR::ABL1 fusion. It is especially helpful if the Philadelphia chromosome is “hidden” and missed by a standard karyotype ^[7].
• Quantitative BCR::ABL1 RT-PCR: This highly sensitive test identifies your specific BCR::ABL1 transcript type (usually letter-number codes like e13a2 or e14a2) ^[8][9]. It establishes a baseline of your leukemia on the International Scale (%IS). The %IS is a standardized ratio used to track how well your treatment is working over time, not a literal count of every leukemia cell in your body ^[10]. Note that rare, atypical transcripts might require custom lab assays and cannot always be reported on the standard %IS ^[11].

Physical Exams and Baseline Health Checks

TKIs are highly effective, but different drugs have different side-effect profiles. Your team evaluates your overall health to match you with the safest option ^[12][13].

• Spleen Assessment: CML often causes an enlarged spleen. Your doctor will typically measure it during a physical exam by feeling how many centimeters it extends below your ribs ^[14]. Imaging, like an ultrasound, is only used if the exam is unclear or there are specific concerns ^[15].
• Baseline Blood Chemistry and Lipids: Blood tests will check your liver and kidney function, electrolytes, blood sugar, and a lipid panel for cholesterol ^[1][16].
• Cardiovascular Evaluation: Depending on your health history and the specific TKI planned, your doctor may check your blood pressure and recommend an electrocardiogram (ECG) to measure your heart’s electrical activity ^[17][18].
• Reproductive Health: Because TKIs can affect fetal development, it is vital to discuss pregnancy plans, fertility preservation, contraception, and breastfeeding before starting treatment.

This baseline health snapshot is crucial. For example, the TKI nilotinib can increase the risk of high blood sugar, elevated cholesterol, and vascular disease, while ponatinib is associated with high blood pressure and vascular risks ^[16][19]. Your doctor will use your health history to choose a drug that minimizes your personal risks ^[12][18].

Determining Your Disease Phase and Risk Score

Your complete results help establish two vital pieces of information:

The Phase of Your CML

CML is classified into phases based on blood counts, blast percentages, and whether leukemia blasts have formed tumors outside the marrow (extramedullary blast proliferation) ^[4][20].

• Chronic Phase: The earliest and most common phase, typically involving fewer than 10% blasts ^[4].
• Accelerated Phase: An intermediate phase marked by rising blasts (often 10–19%), high basophils, or persistent blood count changes. Note that some newer medical guidelines omit this phase entirely ^[21].
• Blast Phase: The most advanced phase. Depending on the specific medical guidelines your doctor follows (such as WHO or ELN), this is defined by having either 20% or 30% or more blasts, or by extramedullary blast proliferation ^[4][21][20].

The ELTS Risk Score

If you are in the chronic phase, your doctor will calculate your EUTOS Long-Term Survival (ELTS) score ^[22]. This uses a formula combining four variables:

1. Your age
2. The size of your spleen (measured by physical exam)
3. Your platelet count
4. The percentage of blasts in your blood

The ELTS score categorizes statistical group risk (low, intermediate, or high) for long-term outcomes ^[22]. It is an estimate to help guide treatment, not a definitive prediction of your individual future.