This may be done by polymerase chain reaction (PCR), fluorescent in situ hybridization (FISH), or conventional cytogenetics of peripheral blood or bone marrow. This mutation involves a translocation of the long arm chromosomes of 15 and 17. On rare occasions, a cryptic translocation may occur which cannot be detected by cytogenetic testing; on these occasions PCR testing is essential to confirm the diagnosis.[1] Presence of multiple Auer rods on peripheral blood smear is highly suggestive of acute promyelocytic leukemia.