All the patients had different degrees of periodontitis (mild 9.2%, moderate 72.4%, severe 18.4%); PPD was inversely related to serum albumin (r = − 0.235, p = 0.041); CAL has a positive correlation with serum C-reactive protein (rs = 0.242, p = 0.035); PLI was positively correlated with serum calcium (r = 0.314, p = 0.006). This evidence concerns the gene CRP and periodontitis.