Sampling
At baseline and at 3- and 6 months after NSPT, blood samples from each patient were taken between 8:00 and 10:00 a.m., before any periodontal examination. Following sampling, serum samples were centrifuged at 4 °C (1000x g for 2 min) and stored. The serum GDF-15, GPx-1, and SP-D concentration levels were obtained using a specific kit according to the manufacturer’s instructions and were evaluated using human-specific enzyme-linked immunosorbent assay (ELISA) kits. The hs-CRP levels were obtained by a nephelometric assay kit.