[Development of highly sensitive assay for detection of low serum level of PIVKA-II and its clinical usefulness].

PIVKA-II is well known as a tumor marker of hepatocellular carcinoma. We describe the adaptations to render a commercially available PIVKA-II immunoassay kit (Eitest MONO P-II: Eisai Co., Ltd, Tokyo) more sensitive and evaluated clinical usefulness of this highly sensitive assay for early diagnosis of hepatocellular carcinoma. We measured serum PIVKA-II concentrations with the Eitest kit as described for the kit. To measure serum PIVKA-II concentrations below the sensitivity limit of the Eitest kit (0.0625AU/ml), linearity was determined using a series of dilutions of standard antigen diluted in standard diluent, including PIVKA-II concentrations of 0.002, 0.004, 0.008, 0.016, 0.031, 0.0625AU/ml. The assay was found to be liner from 0.004AU/ml. In this way, one can detect as low PIVKA-II concentrations as 0.004AU/ml. The repeatability-assay coefficients of variation (CV%) obtained from sixteen repeated assays of four sera were distributed between 3.63 and 18.75% and the reproducibility-assay coefficients of variation (CV%) obtained from ten repeated assays of four sera were distributed between 6.27 and 14.04%. We determined the serial changes in serum PIVKA-II levels of two patients with hepatocellular carcinoma after the resection of hepatic tumor. In these patients, elevation of serum PIVKA-II level determined by the highly sensitive assay preceded the detection of relapse by imaging diagnostic procedures. In summary, the assay system we developed has good accuracy and reproducibility for assaying low concentrations of PIVKA-II in serum and is suitable for detecting small increases in PIVKA-II concentrations. This assay system may be useful to earlier detect a relapse of hepatocellular carcinoma.