NLR is simply a calculation based on the Absolute Neutrophil Count divided by the Absolute Lymphocyte Count determined by the peripheral blood CBC differential
Under physiologic stress, the number of neutrophils increases, while the number of lymphocytes decreases.
Endogenous cortisol and catecholamines may be major drivers of the NLR.
Increased levels of cortisol are known to increase the neutrophil count while simultaneously decreasing the lymphocyte count.
Likewise, endogenous catecholamine may cause leukocytosis and lymphopenia.
Cytokines and other hormones are also likely to be involved.
Thus, NLR is not solely an indication of infection or inflammation. Any cause of physiologic stress may increase the NLR
Interpretation
Interpretation of NLR depends on clinical context.
A normal NLR is roughly 1-3.
An NLR of 6-9 suggests mild stress
Critically ill patients will often have an NLR of ~9 or higher (occasionally reaching values close to 100).
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