LYMPHOCYTE -TO- MONOCYTE AND PLATELET -TO- LYMPHOCYTE RATIOS AS SEX - DEPENDENT BIOMARKERS OF SUBCLINICAL INFLAMMATION IN PASSIVE SMOKERS

Abstract

Passive smoking is often overlooked in clinical practice but does cause a long-lasting systemic inflammatory burden which can be detected by routine haematological indices which are low cost and inexpensive. The lymphocyte to monocyte ratio (LMR) and platelet to lymphocyte ratio (PLR) have been reported on in active smokers, but have not been studied in adult passive smokers, and not studied in sex specific stratification. The purpose of the present study was to compare LMR and PLR between passive smokers and healthy non smokers adults and to see the relationship between LMR and PLR with duration of passive exposure by dividing the samples based on sex. The current study is a cross sectional study that is comparative in nature and was conducted in Saladin Governorate, Iraq from February till May 2026. There were 28 Passive Smokers (18 male and 10 female) and 30 healthy controls (17 male and 13 female) over an age range of 25-45 years. Venous complete blood counts (CBC) were used to obtain both ratios. Data were analyzed statistically using SPSS version (26.0) and the Pearson correlation coefficient was used to determine the relationships between the exposure duration and the study indices, while independent samples t tests were used to determine the relationship between the duration of exposure and the study indices. The significance level was decided at P ≤ 0.05. Aggregate level results - There was no significant difference between the LMR of passive smokers and controls (7.11 ± 0.60 vs. 7.12 ± 0.38, P = 0.989). Upon stratification, however, LMR was markedly lower in passively exposed females (5.17 ± 0.41 vs. 6.60 ± 0.51, P = 0.030), whereas it showed a non significant elevation in passively exposed males (8.19 ± 0.81 vs. 7.58 ± 0.54, P = 0.237). The overall passive smoking group had a significantly lower level of PLR (98.81 ± 6.14 vs. 110.27 ± 4.85, P = 0.049) but this was not significant in the sex specific sub-analyses. Of note, a negative correlation between LMR and duration of passive smoke exposure was found (r = −0.27, P = 0.047); this was not the case for PLR (r = 0.06, P = 0.867). There is a recognizable systemic inflammatory signature in passive smoking that seems to differ in level of expression depending on the length of exposure to passive smoking and sex. Analysis by sex appears to be most sensitive in LMR, highlighting the importance of disaggregating data by sex. These results suggest that LMR and PLR could be useful early, inexpensive screening tools, but future, more definitive studies are needed to confirm this.