Crevicular fluid is a serum ultrafiltrate that accumulates in gingival connective tissue resulting from increased vascular permeability. When its production increases, it passes to the gingival crevice.
Gingival crevicular fluid contains products derived from microbial plaque, tissue breakdown, host cells, and host immunity that, in some instances, have been demonstrated to be related to the active phases of periodontal destruction.
Aspartate aminotransferase (AST) is an enzyme normally confined to cell cytoplasm, but is released to the extracellular environment upon damage. AST levels in serum and other body fluids ( cerebrospinal fluid, arthritic joint fluids) have been used for several decades as a laboratory diagnosticaid for assessing tissue destruction (i.e.MI, hepatitis). Furthermore, the amount of AST activity observed generally reflects the
extent of cell death and, consequently, the magnitude of tissue destruction. AST activity greatly depends on cellular damage in periodontal tissues. Levels of various inflammatory cytokines can also be determined in GCF.