ObjectiveTo investigate the significance of high-sensitive polymerase chain reaction （PCR） in detecting hepatitis B virus （HBV） among the population with a very low viral load （HBV DNA 10‍ — ‍99 IU/mL）. MethodsThis study was conducted among the chronic hepatitis B （CHB） patients who were treated with nucleos（t）ide analogues for ≥48 weeks in The Fifth Affiliated Hospital of Guangzhou Medical University from September 2019 to February 2022 and had an HBV DNA load below the lower limit of ordinary-sensitivity detection （100 IU/mL）. Then high-sensitivity HBV DNA detection was performed for all patients， and according to these results， the patients were divided into very low viral load group （VLVL group with an HBV DNA load of 10‍ — ‍99 IU/mL） and complete virologic response group （CVR group with an HBV DNA load of <10 IU/mL or without HBV DNA detected）. The two groups were compared in terms of general characteristics， serum virological indicators， biochemical parameters， and noninvasive fibrosis markers； the value of related serum virological indicators in predicting the results of high-sensitivity HBV DNA above the lower limit of detection were assessed； the influencing factors for failure to achieve CVR were analyzed. The independent-samples t test was used for comparison of normally distributed continuous data between two groups， and the Mann-Whitney U test was used for comparison of non-normally distributed continuous data between two groups； the chi-square test or the Fisher’s exact test was used for comparison of categorical data between two groups. The receiver operating characteristic （ROC） curve was used to investigate the value of related serum virological indicators in predicting the results of high-sensitivity HBV DNA above the lower limit of detection， and a binary logistic regression analysis was used to investigate the influencing factors for failure to achieve CVR. ResultsA total of 106 CHB patients were enrolled， with 24 in the VLVL group and 82 in the CVR group. Compared with the CVR group， the VLVL group had a significantly younger age （P=0.004） and significantly higher quantitative hepatitis B surface antigen （qHBsAg） level （P=0.002）， HBeAg positive rate （P=0.002）， pgRNA positive rate （P=0.010）， and alanine aminotransferase level （P=0.017）. The qHBsAg level had an area under the ROC curve of 0.717 （P=0.002） in predicting the results of high-sensitivity HBV DNA above the lower limit of detection （>10 IU/mL）， with an optimal cut-off value of 1 214.5 IU/mL， a sensitivity of 95.5%， and a specificity of 53.9%. Positive HBeAg （odds ratio ［OR］=3.654， 95% confidence interval ［CI］： 1.162‍ —‍ ‍11.489， P=0.027） and qHBsAg （OR=2.985， 95%CI： 1.058‍ — ‍8.422， P=0.039） were independent influencing factors for failure to achieve CVR. ConclusionSome CHB patients have an HBV DNA load of <100 IU/mL by ordinary-sensitivity detection， but with the presence of VLVL determined by high-sensitivity PCR. The VLVL group had significantly higher level of inflammatory damage and positive rates of pgRNA and HBeAg. Positive HBeAg and high qHBsAg level are independent influencing factors for failure to achieve CVR. Clinicians should not ignore the presence of VLVL in CHB patients， and high-sensitivity HBV DNA detection should be performed in a timely manner.