The labelling index is the percentage of myeloma cells incorporating tritiated thymidine during a one hour flash label. A low labelling index is associated with a stable course, while a high labelling index is associated with a more rapid disease progression.
Specimen: Originally performed on bone marrow specimens. It can also be performed on peripheral blood.
labelling index, as a percent =
= ((number of myeloma cells incorporating thymidine) / (total number of myeloma cells)) * 100
Bone Marrow LI
Survival
> 3%
increased, associated with reduced survival (5.3 months)
>= 2%
16 months median survival, and short median remission duration
< 2%
47 months
Interpretation:
• An increase in the LI often precedes relapse.
• An LI < 1% can seen in MGUS and indolent myeloma.
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