Under physiologic stress, the number of neutrophils increases, while the number of lymphocytes decreases. The Neutrophil:Lymphocyte Ratio (NLR) combines both of these changes, making it more sensitive than either alone. Endogenous cortisol and catecholamines (e.g. adrenaline) are significant drivers of the NLR. Increased levels of cortisol increase the neutrophil count while simultaneously decreasing the lymphocyte count.​​ The NLR is not solely an indication of infection or inflammation, and any cause of stress may increase it (e.g. severe dehydration).