What definitive step is involved in the diagnosis of Chronic Myeloid Leukaemia (CML)?

The definitive step in the diagnosis of Chronic Myeloid Leukaemia (CML) is the genotype study, specifically the detection of the Philadelphia chromosome or the BCR-ABL fusion gene. This genetic abnormality results from a translocation between chromosomes 9 and 22 and is considered the hallmark of CML. The presence of this chromosome confirms the diagnosis, allowing healthcare providers to not only establish the condition but also to tailor subsequent treatment options effectively.

While a complete blood count can indicate abnormalities suggestive of CML, and bone marrow aspiration provides important cellular information, these methods alone do not confirm the diagnosis with the same level of specificity as a genotype study. Similarly, a peripheral blood smear can show signs of leukaemia, such as immature white blood cells, but it cannot definitively identify the underlying genetic changes that characterize CML. Therefore, the genotype study is crucial for accurate diagnosis and management of the disease.