In medicine neutrophil to lymphocyte ratio (NLR) is used as a marker of subclinical inflammation. It is calculated by dividing the number of neutrophils by number of lymphocytes, usually from peripheral blood sample,^[1] but sometimes also from cells that infiltrate tissue, such as tumor.^[2] Recently Lymphocyte Monocyte ratio (LMR) has also been studied as a marker of inflammation including tuberculosis and various cancers.

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A 2017 study found that the normal NLR range for healthy adults is between 0.78 and 3.53.^[11]

Neutrophil to Lymphocyte ratio was first demonstrated as useful parameter after a correlation of a relationship between the neutrophil lymphocyte ratio to reactions of the immune response was noted. A study in 2001 was conducted by the Department of Anaesthesiology and Intensive Care Medicine, St. Elizabeth Cancer Institute in Bratislava by Zahorec which suggested the routine used of the ratio as a stress factor in clinical ICU practice in intervals of 6-12 and 24 hours.^[12]

The first study to demonstrate that pretherapuetic NLR can be used as a predictor of chemotherapy sensitivity to thoracic esophageal cancer was demonstrated by Hiroshi Sato, Yasuhiro Tsubosa, and Tatsuyuki Kawano in a 2012 study published in World Journal of Surgery journal.^[13]