A systematic review and meta-analysis was conducted to investigate the relevance of the neutrophil to lymphocyte ratio (NLR) in the context of Parkinson's disease (PD).

Electronic databases such as ProQuest, Web of Science, and PubMed were utilized to search for studies that compared NLR between individuals with PD and healthy controls. Two evaluators conducted an independent assessment of the methodological rigor of the included papers by utilizing the Newcastle-Ottawa scale. Subsequently, the standardized mean difference (SMD) was calculated.

Using a random-effect model, it was evident that individuals with PD exhibited heightened NLR values in comparison with their healthy counterparts (SMD = 0.81). Subgroup analysis further revealed the following:

1. In terms of study design, the results indicated that both retrospective (SMD = 1.12) and prospective (SMD = 0.43) studies showed higher NLR levels in PD patients compared to healthy controls.
2. With regard to ethnicity, individuals with PD had increased NLR levels than healthy controls, whether they were of East Asian (SMD = 0.93) or Caucasian (SMD = 0.75) descent.

Additionally, the pooled sensitivity of NLR in predicting PD was 0.67, and the pooled specificity stood at 0.66.

There was a notable connection between elevated NLR levels and the occurrence of PD. Additional investigation is required to ascertain the potential clinical advantages of utilizing this affordable and simple biomarker for diagnosing PD.