Color Atlas of Hematology - Practical Microscopic and Clinical ...

112Abnormalities of the White Cell SeriesReactive Left ShiftA relative left shift in the granulocyte series means less mature forms inexcess of 5% band neutrophils; the preceding, less differentiated cell formsare included and all transitional forms are taken into account. This leftshift almost always indicates an increase in new cell production in this cellseries. In most cases, it is associated with a raised total leukocyte count.However, since total leukocyte counts are subject to various interferingfactors that can also alter the cell distribution, left shift without leukocytosiscan occur, and has no further diagnostic value. At best, if no other explanationsoffer, a left shift without leukemia can prompt investigation forsplenomegaly, which would have prevented elevation of the leukocytecount by increased sequestration of leukocytes as in hypersplenism.In evaluating the magnitude of a left shift, the basic principle is that themore immature the cell forms, the more rarely they appear; and that thereis a continuum starting from segmented granulocytes and sometimesreaching as far as myeloblasts. Accordingly, a moderate left shift of mediummagnitude may include myelocytes and a severe left shift may go asfar as a few promyelocytes and (very rarely) myeloblasts, all depending onhow fulminant the triggering process is and how responsive the individual.The term “pathological left shift” (for a left shift that includespromyelocytes and myeloblasts) is inappropriate, because such observationscan reflect a very active physiological reaction, perhaps following a“leukemoid reaction” with pronounced left shift and leukocytosis.Causes of Reactive Left ShiftLeft shift occurs regularly in the following situations:➤ Bacterial infections (including miliary tuberculosis),➤ Nonbacterial inflammation (e.g., colitis, pancreatitis, phlebitis, andconnective tissue diseases)➤ Cell breakdown (e.g., burns, liver failure, hemolysis)Left shift sometimes occurs in the following situations:➤ Infection with fungi, mycoplasm, viruses, or parasites➤ Myocardial or pulmonary infarction➤ Metabolic changes (e.g., pregnancy, acidosis, hyperthyroidism)➤ Phases of compensation and recuperation (hemorrhages, hemolysis,or after medical or radiological immunosuppression).