Issues of TCR PCR test result interpretation are related to the method used to evaluate the PCR product. In gel-based assays, a positive result is based on finding a discrete band of the appropriate size in contrast to a smear or ladder of bands found with polyclonal T cells. With capillary elec-trophoresis instruments, each laboratory must establish and validate its own criteria for a positive result. The most commonly used criteria consider a peak that is two (or three) times larger than the third-largest peak to be evidence of a monoclonal population. This approach allows for biallelic rearrangements that may show two clonal peaks. Less-stringent criteria can be used with capillary electrophoresis in follow-up samples when the size of the expected clonal PCR product is known from prior testing.
Oligoclonal proliferations offer additional interpretive challenges. The presence of more than two bands on a gel (or more than two prominent peaks by capillary elec-trophoresis) should be considered evidence of an oligo-clonal proliferation rather than monoclonality. Variation in the size of the bands or peaks on duplicate runs of the same sample should be interpreted as evidence of oligoclonality (or selective amplification of small numbers of polyclonal T cells in a paucicellular sample). For this reason,many laboratories test samples in duplicate to confirm the repro-ducibility of a monoclonal population before reporting a positive monoclonal result.
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