Abstract: Objective To analyze the clinical characteristics and nucleic acid testing (NAT) to guide the interpretation of gray zone (GZ) sample results detected by chemiluminescence technology. Methods The results of patients admitted to 5 general hospitals in different regions of the country from July to December 2021 were collected for Transfusion Transmissible Infection (TTI) screening tests before surgery/transfusion. NAT detection and clinical characteristics analysis were performed on GZ samples. Results Among the 5 723 samples, 28 (0.49%) were GZ for HBV and 20 (0.35%) for HCV. NAT results showed that 15 of the 28 HBV GZ (53.5%) were NAT-positive, and their HBcAb were all positive; 13 HBV samples (46.5%) were NAT-negative, of which 4 positive for HBcAb. HBV and HCV GZ samples were found in all clinical departments. The top three departments of HBV GZ samples were orthopedics, gynecology, and urology and the largest number of false positives were gynecology and orthopedics. The top three departments for HCV GZ samples were urology, nephrology, and surgery, and all of them were false positives. 35.7% (10/28) of patients with HBV GZ samples and 40% (8/20) of patients with HCV GZ samples were diagnosed as neoplastic diseases. Conclusion Chemiluminescence methods are prone to false-positive results, so attention should be paid to retest for verification and it is not necessary to set up GZ. Gz samples can be found in some clinical departments exhibiting specific clinical distribution characteristics. NAT can improve detection sensitivity and ensure accuracy to verify GZ.

Key words: Hepatitis B virus, Hepatitis C virus, Human immunodeficiency virus, Chemiluminescence immunoassay, Gray zone, Nucleic acid testing