Fluorescence in situ hybridization (FISH)

is another test used to detect the Philadelphia chromosome and the BCR-ABL fusion gene. This test may be used on a peripheral blood sample if a bone marrow sample can’t be collected. FISH uses color “probes” to find the BCR gene and the ABL gene in chromosomes. The BCR-ABL fusion gene, located on the Philadelphia chromosome, is shown by the overlapping colors of the two probes. FISH analysis of peripheral blood may be used to diagnose CML when bone marrow cytogenetics isn’t possible. But, FISH is not recommended for monitoring the response to treatment.