- Last Update On : 2017-01-24
The absolute neutrophil count (ANC) is equal to the product of the white blood cell count (WBC) and the fraction of polymorphonuclear cells (PMNs) and band forms noted on the WBC differential analysis:
ANC = WBC (cells/microLiter) x percent (PMNs+bands)/100
Recurrent infections are the only significant consequence of neutropenia. The propensity to infection is related to the ANC level and the duration of neutropenia.
Neutropenia is often categorized as mild, moderate or severe, based upon the level of ANC. Mild neutropenia corresponds to an absolute neutrophil count between 1000 and 1500/microL, moderate between 500 and 1000/microL, and severe with less than 500/microL. The risk of infection begins to increase at an ANC below 1000/microL.
Patients with an ANC <500/microL due to chemotherapy are at high risk for bacterial infection. This is particularly true in cancer patients with an ANC <100/microL for more than five days. The source of microbial invasion of the blood is chemotherapy-induced mucositis and breaks in the gastrointestinal lining.
The most common bacteria that infect neutropenic patients are endogenous bacteria, including Staphylococcus aureus from the skin and Gram negative organisms from the gastrointestinal and urinary tract. Isolated neutropenia does not increase the susceptibility to viral or parasitic infection.
Common sites of infection include the oral cavity and mucous membranes, the skin, and perirectal and genital areas. With persistent severe neutropenia, systemic infection occurs associated with bacteremia, and infections of the lung and gastrointestinal tract. Patients receiving broad spectrum antibiotics for two weeks or more while neutropenic are more prone to infection with enteric bacteria and/or fungi, while patients with indwelling catheters or other foreign bodies are more likely to become infected with coagulase-negative staphylococci.
In general, patients with an ANC greater than 1000/microL can be managed on an outpatient basis while those with an ANC of less than 500/microL and marrow aplasia should always be treated on an inpatient basis with parenteral antibiotics.