Apical periodontitis(AP) develops as a result of the host’s immune inflammatory response to pulpal infection of the dental root canals that leads to the generation of an apical lesion of endodontic origin(ALEO) and potentially to systemic metabolic alterations. Misdiagnosed ALEO is not infrequent due to the lack of diagnostic tools to differentiate apical lesions of different natures. Despite the conservative endodontic treatment shows a high success rate, there are refractory cases that can not be identified early enough during follow up. This evidences the need to develop complementary diagnostic tools, such as oral fluid biomarker analysis. Gingival crevicular fluid(GCF) is a serum transudate that becomes an exudate under inflammatory conditions, carrying molecules from local periodontal tissuesand general circulation than can be harvested noninvasively. We aimed to review the available literature analyzing GCF composition in AP patients to evaluate whether GCF has any potential for complementary diagnosis. To the date, only few studies addressing changes of GCF components in AP are available. Most studies support GCF modifications in specific components in APaffected teeth, suggesting that it might reflect periapical inflammation. GCF has potential for diagnostic tool, treatment follow-up and eventually to assess systemic comprise. Apical periodontitis (AP) develops as a result of the host’s immune inflammatory response to pulpal infection of the dental root canals that leads to the generation of an apical lesion of endodontic origin (ALEO) and potentially to systemic metabolic alterations. Misdiagnosed ALEO is not infrequent due to the lack of diagnostic tools to differentiate apical lesions of different natures. Despite the conservative endodontic treatment shows a high success rate, there are refractory cases that can not be identified early enough during follow up. This evidences the need to develop complementary diagnostic tools , such as oral fluid biomarker analysis. Gingival crevicular fluid (GCF) is a serum transudate that becomes an exudate under inflammatory conditions, carrying molecules from local periodontal tissues and general circulation can be harvested noninvasively. We aimed to review the available literature analyzing GCF composition in AP patients to evaluate whether GCF has any potential for To recommend the GCF components in AP are available. Most studies support GCF modifications in specific components in APaffected teeth, suggesting that it Might reflect periapical inflammation. GCF has potential for diagnostic tool, treatment follow- up and eventually to assess