Detection of free hepatitis C virus core antigen by enzyme-linked immunosorbent assay is not suitable for screening of granulocyte colony-stimulating factor-mobilized hematopoietic progenitor donors

BACKGROUND: Recent studies have shown that hepatitis C virus (HCV) can be detected in peripheral blood mononuclear cells of patients who are negative for the presence of anti-HCV and serum HCV RNA. The aim of the study was to evaluate the prevalence of HCV viremia in granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood progenitor cell (PBPC) donors by the use of a free HCV core antigen enzyme-linked immunosorbent assay (ELISA). STUDY DESIGN AND METHODS: A total of 28 samples from consecutive PBPC donors that were mobilized with G-CSF, and 13 samples from patients presenting with leukocytosis of greater than 20 x 109 per L from other causes, were tested by a free HCV core antigen ELISA. Positive samples were confirmed by use of neutralization assays. The specificity of the assay was studied in 48,911 healthy blood donors negative for the presence of anti-HCV. RESULTS: The free HCV core antigen assay showed a 46.4 percent positivity in PBPC donors mobilized with G-CSF and 61.5 percent in patients exhibiting leukocytosis in the absence of G-CSF treatment. All the samples were found to be false-positive samples, and those related with growth factor treatment did not react when G-CSF was discontinued. Overall specificity by the test in freshly collected blood donor specimens was 99.62 percent. CONCLUSION: Data indicate that the free HCV core antigen ELISA is not a valid test in diagnosing HCV infection in G-CSF-treated PBPC donors. Moreover, false-positive results of this test on blood donors might be indicative of elevated white blood cell numbers. The low specificity of this assay in the PBPC mobilization setting suggests that molecular assays should be the test of choice in the screening of G-CSF-treated donors.