Typically, the allelic profiles of amplified DNA from matching normal and test samples are compared. The detection of novel alleles in the test sample that are absent in the matching normal sample is an indication of MSI.
MSI-positive for a marker is recognized as alterations in the lengths of the microsatellite due to deletion or insertion of a repeating nucleotide unit, which produces a novel length allele in test DNA compared to matching normal DNA.
Data from five microsatellite loci are assessed.
Definition of MSI-High: Instability in 2 or more of the loci
The results for MSI analysis can be provided using two formats: