The left shift index: A useful guide to the interpretation of marrow data

Abstract

Some acute conditions, whether naturally occurring or induced during the course of a toxicity study, lead to a series of dynamic changes in the bone marrow. These are frequently monitored by the use of the myeloid:erythroid ratio (M:E ratio). However, in the early stages of an acute reaction, the increase in numbers of primitive and early cells, stimulated by the reaction, is frequently counterbalanced by the release of mature or nearly mature cells from the marrow to their appropriate active sites, thus leaving the M:E ratio unchanged, or even apparently moving in the ‘wrong’ direction'. In an attempt to quantify these early changes, the Left Shift Index was devised for both myeloid and erythroid cells. Application of these indices to a series of toxicity studies, and to a specific diagnostic situation, shows that they can be both predictive and diagnostic, in contrast to the M:E ratio, which can often give a misleading impression.