Assessment of neutrophilia

Neutrophilia may occur with or without an elevated white blood cell (WBC) count. Neutrophilia without leukocytosis is defined as an elevated circulating neutrophil count (>7.7×10⁹/L) in adults with a normal total WBC count of <11×10⁹/L.[1]Hoffman R, Benz E, Silberstein L, et al. Hematology basic principles and practice. 7th ed. Philadelphia, PA: Elsevier Churchill Livingston; 2017. An elevated total WBC count (>11×10⁹/L) and an absolute neutrophil count >7.7×10⁹/L is defined as a neutrophilic leukocytosis.[1]Hoffman R, Benz E, Silberstein L, et al. Hematology basic principles and practice. 7th ed. Philadelphia, PA: Elsevier Churchill Livingston; 2017.

The absolute neutrophil count can be estimated by multiplying the total WBC count by the percentage of polymorphonuclear cells and band forms (immature neutrophils have a band-shaped nucleus).[2]Levy MM, Fink MP, Marshall JC, et al. 2001 SCCM/ESICM/ACCP/ATS/SIS International Sepsis Definitions Conference. Crit Care Med. 2003 Apr;31(4):1250-6. http://www.ncbi.nlm.nih.gov/pubmed/12682500?tool=bestpractice.com

The terms granulocytosis and neutrophilia are often used interchangeably, although granulocytosis also includes elevations in eosinophils and basophils.

The terms hyperleukocytosis and leukaemoid reaction are reserved for total leukocyte counts of >50×10⁹/L. Leukaemoid reaction may mimic leukaemia, but has a non-malignant aetiology.

Neutrophilia results from:

• Increased production of neutrophils

• Demargination (process of neutrophils entering the peripheral circulation from areas of intravascular marginated polymorphonuclear cell pools), or

• Decreased egress (outwards migration) of neutrophils from peripheral circulation to the tissues.[Figure caption and citation for the preceding image starts]: NeutrophiliaFrom the collection of T. George, MD [Citation ends].

Epidemiology

Many diverse factors contribute to the development of neutrophilia, so defining the population at risk is difficult. Leukocyte and neutrophil counts in health exhibit some racial differences. Hispanic people in the US have been shown to have a higher leukocyte count (mean difference 0.16×10⁹/L) and higher neutrophil count (mean difference 0.11×10⁹/L) relative to white people.[3]Hsieh MM, Everhart JE, Byrd-Holt DD, et al. Prevalence of neutropenia in the US population: age, sex, smoking status, and ethnic differences. Ann Intern Med. 2007 Apr 3;146(7):486-92. http://annals.org/article.aspx?articleid=733880 http://www.ncbi.nlm.nih.gov/pubmed/17404350?tool=bestpractice.com

The neutrophil count changes with age, with the highest counts seen in the first few days after birth, then decreasing rapidly. Neutrophil counts approach adult levels around age 10. Lifestyle factors, including exercise levels, stress, and smoking status, influence the risk of neutrophilia.