This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
A ratio from a routine blood count
A complete blood count with differential gives the absolute numbers of each type of white blood cell. Dividing neutrophils by lymphocytes gives the neutrophil-to-lymphocyte ratio (NLR), an inexpensive marker of the body’s inflammatory and stress response.
The formulas
- NLR = absolute neutrophils ÷ absolute lymphocytes
- PLR (platelet-to-lymphocyte ratio) = platelets ÷ lymphocytes
- LMR (lymphocyte-to-monocyte ratio) = lymphocytes ÷ monocytes
- SII (systemic immune-inflammation index) = platelets × neutrophils ÷ lymphocytes
- Derived NLR = neutrophils ÷ (white cells − neutrophils), approximated here as neutrophils ÷ (lymphocytes + monocytes)
Use absolute counts, not percentages. In the United States they are usually reported in × 10³/µL, which is numerically the same as × 10⁹/L.
Example
Neutrophils 4.0, lymphocytes 2.0, monocytes 0.5 and platelets 250 (× 10³/µL) give an NLR of 2.0, a PLR of 125, an LMR of 4 and an SII of 500.
| NLR | Usual reading |
|---|---|
| 0.7 to 3 | Normal range in healthy adults |
| 3 to 6 | Mild to moderate stress or inflammation |
| above 6 | Marked stress, such as severe infection or major surgery |
| under 0.7 | Low neutrophils or high lymphocytes |
Why the NLR rises
During acute stress, cortisol and catecholamines mobilize neutrophils and send lymphocytes out of the bloodstream. The NLR therefore rises within hours in bacterial infection, sepsis, trauma or after surgery, often before other markers.
Uses and limits
Studies have linked a high NLR with worse outcomes in sepsis, pneumonia, heart disease and many cancers, where it is used as a prognostic factor. But:
- Cut-offs vary between studies and diseases.
- Corticosteroids, recent exercise, smoking and some drugs change the ratio.
- It is non-specific: it tells you that there is a stress response, not what causes it.
Read it together with the full blood count, the clinical picture and markers such as CRP.