Relationship between Occupational Exposure to Respirable Crystalline Silica and Serum Copper Level as an Indicator of Silicosis: A Systematic Review and Meta-analysis.

Background: This systematic review and meta-analysis study evaluates a relationship between occupational exposure to respirable crystalline silica and serum copper (Cu) levels as an indicator for early detection of silicosis.

Materials and methods: A systematic search was conducted, and the quality of results was evaluated in accordance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses. The following databases were searched, including Web of Sciences, Scopus, and PubMed from inception until November 2021. The following keywords were selected for searching in the mentioned databases including, "copper" OR "serum copper" AND "silicosis". The mean (standard deviation [SD]) of Cu was extracted for both silicosis and non-silicosis subjects. The differences in mean effect size were pooled using the random-effect model. Heterogeneity and publication bias were evaluated using the I² value and Begg's test and Egger's test, respectively.

Results: A total of 159 studies were initially found, among which eight studies were included in the meta-analysis. Random-effect meta-analysis of these eight studies showed that silicosis patients had higher copper levels than the non-silicosis group with a pooled standardized mean difference (SMD) of 3.02 (95% confidence interval: 0.25, 5.78); I² = 99.3%, P value < 0.001. The subgroup analysis showed that the corresponding figures in those with mean age >40 years and <40 years were 5.79 (2.06, 9.52) and -0.43 (-4.57, 3.70), respectively. Moreover, no publication bias was found in the analyses.

Conclusions: The results of the present study demonstrated that silica exposure may be associated with increasing serum Cu levels.