Neutrophil-to-Lymphocyte Ratio (NLR)

Overview

Neutrophil-to-Lymphocyte Ratio (NLR) is a simple, calculated biomarker derived from the ratio of neutrophils to lymphocytes in peripheral blood. It reflects the balance between innate immunity (neutrophils) and adaptive immunity (lymphocytes) and serves as an indicator of systemic inflammation and physiological stress¹². NLR is increasingly used in clinical settings to assess inflammatory status, predict disease severity, and evaluate prognosis in conditions such as infections, cardiovascular diseases, autoimmune disorders, cancer, and critical illness¹³.

Scientific Background

Neutrophils are key cells of the innate immune system, responsible for early defense against pathogens through mechanisms like phagocytosis, reactive oxygen species production, and cytokine release. Lymphocytes, primarily T and B cells, mediate adaptive immune responses. The NLR integrates these two immune components, providing insight into the body"s inflammatory and immune status². Under stress or inflammatory conditions, neutrophil counts typically rise due to activation and delayed apoptosis, while lymphocyte counts often decrease, reflecting immune suppression or redistribution⁴. Hormones such as cortisol and catecholamines modulate these changes, increasing neutrophils and decreasing lymphocytes⁴. Elevated NLR has been linked to systemic inflammatory response syndrome (SIRS), infections, tissue damage, and malignancies, highlighting its role as a marker of both inflammation and physiological stress²¹.

Measurement and Testing

NLR is calculated by dividing the absolute neutrophil count by the absolute lymphocyte count, both obtained from a routine complete blood count (CBC) with differential using automated hematology analyzers³. The test is widely available, rapid, and cost-effective. Factors influencing NLR include acute infections, stress, medications (e.g., corticosteroids), and chronic inflammatory states. Testing is recommended as part of routine blood work when inflammation or immune status assessment is clinically indicated, and it can be repeated to monitor disease progression or response to therapy³⁴.

Reference Ranges

Normal NLR values typically range from approximately 1 to 3 in healthy adults, though exact reference ranges may vary by laboratory and population⁶. Age, sex, ethnicity, and physiological stress can influence baseline NLR. For example, elderly individuals may have slightly higher baseline NLR due to low-grade inflammation. Values above the normal range suggest increased systemic inflammation or stress, while very low values are less common and may indicate lymphocytosis or neutropenia⁶. Interpretation should consider clinical context and other laboratory findings.

High Values

Elevated NLR is caused by increased neutrophil counts and/or decreased lymphocyte counts. Common causes include bacterial or fungal infections, acute and chronic inflammatory diseases, cardiovascular events (e.g., myocardial infarction), cancer, trauma, and systemic inflammatory response syndrome (SIRS)¹². High NLR is associated with worse prognosis in many conditions, including higher mortality risk in cardiovascular disease, cancer progression, and severe infections such as COVID-19¹³. Symptoms related to elevated NLR depend on the underlying cause but may include fever, fatigue, pain, or signs of infection or inflammation.

Low Values

Low NLR values are less frequently discussed but may result from neutropenia (low neutrophil count), lymphocytosis (high lymphocyte count), or both. Causes include viral infections, bone marrow suppression, certain autoimmune diseases, or medication effects. Low NLR may indicate a suppressed innate immune response or an active adaptive immune response. Clinical implications depend on the context; for example, lymphocytosis with low NLR can be seen in viral infections or lymphoproliferative disorders⁶.

Improving Biomarker Levels

Since NLR reflects systemic inflammation and stress, improving its levels involves addressing underlying causes. Lifestyle modifications such as a balanced diet rich in anti-inflammatory foods, regular physical activity, stress reduction, and smoking cessation can help reduce chronic inflammation and normalize NLR¹. Managing chronic diseases effectively and treating infections promptly are critical. In some cases, pharmacologic interventions like anti-inflammatory or immunomodulatory therapies may be necessary. Supplements with anti-inflammatory properties (e.g., omega-3 fatty acids) might support lowering elevated NLR, but clinical evidence is limited and should be guided by healthcare providers¹².

Importance of Tracking

Monitoring NLR provides valuable information about a person"s inflammatory and immune status, aiding early detection of disease progression or complications. It helps clinicians stratify risk, guide treatment decisions, and monitor response to therapy in various conditions, including infections, cardiovascular diseases, and cancer¹³. Because NLR is a simple, inexpensive, and widely available test, it is a practical tool for ongoing patient management and prognostication.

Disclaimer

The information provided in this document is for educational purposes only and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.