Circulating candida antigen - blood test. what is this specifically and is it sensitive? thank you

Probably useless: Testing for Candida antigen in the blood sometimes helps diagnose and follow patients being treated for disseminated candidiasis, i.e. candida sepsis. Such patients are deathly ill and many die. The test does not diagnose candida in outwardly healthy people not hospitalized for sepsis. There is no such thing as "systemic candidiasis": it's an urban myth. Don't waste your money on this.