*2.8. Statistical Analysis*

GraphPad Prism software version 8.01, 2018 (GraphPad Software, San Diego, CA, USA) was used to analyze data. The Mann–Whitney U test was used to determine di fferences in age, body mass index (BMI), and blood Pb concentration in controls versus workers. Di fference in smoking history was determined by odds ratio and chi-square test. Spearman's rank correlation was used to identify the correlations between blood Pb concentration and seven measured immunologic parameters, including proliferation index, percentages of phagocytic cells, levels of cytokines, and percentages of T cell subpopulations. The result was considered statistically significant when *p*-values were less than 0.05 in a two-sided test.
