White blood cells, or WBCs, fight infection within the body. The blood WBC count increases or decreases in response to infection and conditions such as cancer or the use of certain drugs. The relative and absolute numbers of different types of blood WBCs often reflect the type, duration or severity of disease. A number of factors -- including bacterial infections, cancer, stress and chemotherapy -- cause an increase or decrease in numbers of blood neutrophils, a type of WBC. Laboratories report blood neutrophil levels as a percentage of the total WBC count and as a neutrophil concentration or absolute neutrophil count. Information needed to calculate the absolute neutrophil count includes the WBC count and the percentage of WBCs that are neutrophils.
Obtain an absolute WBC count and the percentage of the WBC count attributed to each different type of WBC from your doctor. Laboratories perform either a machine or manual analysis of a blood sample to attain these numbers, often reported as a Complete Blood Count with Differential, or CBC with Differential.
Add together the percentages of segmented neutrophil cells, often listed as neutrophils or polys, and band neutrophils, usually listed as bands. Segmented neutrophils are mature neutrophils; bands are immature neutrophils. The sum represents the total percentage of blood WBC's that are neutrophils.
Multiply the sum by the WBC count, then divide by 100. The result will give the absolute neutrophil count. Report the result as the number of neutrophils per microliter of blood.
For example, if the WBC is 10,000 cells per microliter, the percentage of neutrophils is 10 and of bands is five, then the absolute neutrophil count is [(10 + 5) x 10,000]/100, or 1500 neutrophils per microliter of blood.
Use the correct number for WBC; WBC is often reported as a number times ten to the third power. In the example above, the WBC would be reported as 10.
Most laboratories report the absolute neutrophil count in the CBC with Differential results. Calculation is not needed in these cases.