Traditionally, IgVH SHM has been evaluated by rt-PCR followed by Sanger Sequencing using patient sample RNA. However, RNA lability places a significant burden on the submitting physician to minimize specimen transit time. The Sanger Sequencing approach is also time and labor intensive and may show limited sensitivity in detection of IgVH SHM for low abundance clones. Flow cytometric analysis of ZAP-70 expression has therefore been widely utilized as a surrogate for IgVH SHM status, however, standardization for this marker is known to be poor due to the subjective nature of its interpretation. Significant discordance between ZAP-70 expression patterns and IgVH SHM results may also be seen.
International CLL-IPI working group. An international prognostic index for patients with chronic lymphocytic leukaemia (CLL-IPI): a meta-analysis of individual patient data. Lancet Oncol. 2016 Jun;17(6):779-90.