This test detects only the e13/a2 and e14/a2 fusion forms, which code for the p210 protein. Other fusion forms are not detected, including those containing the BCR e1 exon, which codes for the p190 protein commonly found in acute lymphoblastic leukemia (ALL). If the patient is known to carry an e1/a2 (p190) fusion form, Test: BA190/83336, "BCR/ABL, p190, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Quantitative, Monitoring Assay" should be used for monitoring.
This test should not be used to screen for bcr/abl fusions at the time of diagnosis. Test: BADX/89006, "BCR/ABL, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Qualitative, Diagnostic Assay," which is designed to detect all reported and theoretical BCR/ABL fusion variants, should be ordered for this purpose.
The precision of this assay at low bcr/abl levels is relatively poor, such that inter-run variation can be as high as 0.5 log. Only level changes >0.5 log should be considered clinically significant. For example, if a result is given as 0.1% bcr/abl:abl, then any result between 0.05% and 0.5% should be considered essentially equivalent.
If the results are being used to make major therapeutic decisions, significant changes during monitoring should be verified with a subsequent specimen.
In general, the results of this assay cannot be directly compared with results generated from other PCR assays, including identical assays performed in other laboratories. Monitoring should be performed using the same method and laboratory for each subsequent specimen.
However, the results may be directly compared with results obtained from laboratories reporting results using the international scale. The results of this assay cannot be directly compared with bcr/abl results obtained using FISH technology. FISH measures DNA alleles and PCR-based assays measure mRNA transcripts. Because a single DNA allele can produce many mRNA transcripts, the values are not directly comparable.
Blood is the specimen of choice for monitoring. While most patients show similar bcr/abl levels in blood and bone marrow drawn at the same time, some patients have a consistent difference in the levels in blood and bone marrow such that alternating specimen types during monitoring can lead to confusion.
Assay precision does not appear to be significantly affected by specimen transport or moderate delays in processing. However, in specimens with very low levels of bcr/abl these conditions may cause sufficient RNA degradation to produce false-negative results. Thus, specimens should be shipped as quickly as possible and specimens >3 days old at the time of receipt will be considered unacceptable.