This correlation was similar to that between PICF calprotectin amount determined by ELISA and PD value (ρ = 0.709, P < 0.001) [11], and was stronger than the correlation between GCF calprotectin amount and PD in a diagnosis of periodontitis using the same IC chip (ρ = 0.557, P < 0.001) [23], and between the levels of TNF-α or AST activity and PD [38, 39]. Here, TNF is linked to periodontitis.