When you get your blood tested, there are three main counts that doctors look at: red blood cells, white blood cells and platelets. White blood cells are of particular interest as they act as the body's first line of defense against infectious diseases and harmful foreign substances. These cells are further categorized into different types of white blood cells, including the total count, neutrophils, eosinophils, basophils, lumphocytes and monocytes. Considering them in that order, when the percentages increase on the first few types and decrease on the latter types, it is known as a left shift.
Determine the baseline values for each of these types of white blood cells, as well as the total white blood cell count. The total count for a healthy adult is anywhere between 4,000 and 11,000 cells per microliter, according to medterms.com.
Calculate the percentages of each white blood cell type in the following order: neutrophils, eosinophils, basophils, lumphocytes then finally monocytes. This is done by dividing the individual counts of each type by the total white blood cell count.
Take a second blood sample when the patient is sick. The total white blood cell count should be significantly higher than the baseline.
Calculate the percentages of white blood cell types, paying particular attention to the neutrophils. When a patient is suffering from one of a number of ailments, including eclampsia, gout, rheumatoid arthritis, leukemia and trauma, among others, the percentages of white blood cell types will change. The calculated distribution will shift to the left with elevated neutrophil counts.
In the days when test results were written down by hand, the neutrophil percentage was conventionally the first type written down. Because our writing is recorded from left to right, when the neutrophil count is increased, it became known as a left shift.