In one sentence
Neutrophils divided by lymphocytes, the simplest reading of the balance between the immune system's first responders and its regulators, from a blood count you already have.
Why it matters
It is the cheapest inflammation ratio in medicine and the simpler cousin of the Systemic Immune-Inflammation Index, and its reference range in healthy people was measured directly: in 413 working adults aged 21 to 66 attending a health-prevention program, the mean ratio was 1.65 and the 95 percent limits ran from 0.78 to 3.53, confirmed in a second healthy group on different analyzers (Forget 2017). Values above about 3 are where the clinical literature starts to read the balance as tilted, which the clinician specification states as the reference point; the cohort findings for the index above apply to the ratio in the same direction and at the same strength.
What moves it
An infection or injury (up within hours), hard exercise (up for hours), acute psychological stress (lymphocytes fall), smoking, corticosteroids, time of day, and age. It settles within a week or two of whatever moved it.
How to measure it well
From a blood count taken under the panel's rules; the morning, rested, well for two weeks, no hard training for 48 hours. Compare draws taken the same way.
How Vitality Tracker uses it
Computed from one draw only and shown on the labs dashboard beside the counts and the index, with the healthy-adult limits from the Belgian study shown as that study's and the clinical reference point of about 3 as the specification's, never as VT's verdict. No working optimal line is drawn; a draw taken while unwell is excluded.
How far to trust the number
Calculated from two precise counts; the variation is biological and large, so one ratio outside the healthy limits is a reason to repeat the count when well, not a finding.
Sources
- Forget P, Khalifa C, Defour JP, Latinne D, Van Pel MC, De Kock M. What is the normal value of the neutrophil-to-lymphocyte ratio? BMC Res Notes 2017;10:12. doi:10.1186/s13104-016-2335-5
- Xia Y, et al. J Clin Med 2023. doi:10.3390/jcm12031128
- Vitality Tracker, Clinician report content specification (derived indices).