感染症診断に必要な各種マーカーの臨床的意義と評価

Clinical significance and evaluation of various markers necessary for diagnosis of infections

感染症診断の標準法は培養検査あるいは抗原検出による病原体の直接検出である．しかし，培養検査は微生物の発育までに時間を要し，発育が困難・不可能な病原体も多く，抗原の検出にも限界があるため抗体検出，遺伝子検出，検体の鏡見検査などが用いられている．今回は感染症診断を補助する前述以外の関連検査について述べる．CRP，PCTおよびサイトカインは病原体に反応し患者生体内で産生される蛋白質である．炎症性疾患のマーカーとなるが，単独の検査項目として感染症診断の確定にはいたらない．一方，エンドトキシンおよび1,3-β-D-グルカンは病原体の一部を検出する方法で，基準値以上を示す場合は，原因微生物をある程度推定することが可能である．いずれの項目においても患者の病態，病原体の検出を同時に行うことが正確な感染症診断に必須である．

The standard method for the diagnosis of infections is cultivation or direct detection of pathogen antigens.　However, the cultivation test is time-consuming.　In addition there are some pathogens whose growth is difficult or impossible to detect and there is a limit to detecting antigens of many pathogens.　At present the detection of the pathogen antibodies or genes and microscopic examination of test specimens are used for the diagnosis of infections.　The present paper describes test methods other than the above-mentioned methods that assist in the diagnosis of infections.　CRP, PCT and cytokines are proteins that respond to the pathogens and are produced in vivo in the patients.　These proteins are available as markers for inflammatory disease but not available as a single test item in making the diagnosis of infections.　On the other hand, the causative microorganisms can be presumed to some extent by near-cutoff values of endotoxin or 1,3-β-D-glucan which were structural components of pathogens.　It is essential for the exact diagnosis of infections to grasp the pathological condition of patients and to detect the pathogens at the same time in any of the subjects.