Reproducibility of hepatitis C virus antibody detection with various confirmatory assays

Improved efficiency of national HIV, HCV, and HTLV antibody testing algorithms based on sequential screening immunoassays

BACKGROUND

Traditional strategies for clarifying the antibody status of donors giving repeatedly reactive (RR) results on primary screening immunoassays (IA1) have usually involved direct testing by immunoblot. However, such strategies can generate nonspecific in determinate results. The aim of this report is to present the results of an alternative strategy based on the use of sequential immunoassays (SI) before immunoblot testing.

STUDY DESIGN AND METHODS

The efficiency of traditional and SI strategies was compared in terms of the number of IA1 RR samples requiring immunoblot testing and the percentage of immunoblot tests giving indeterminate results. In addition, the biologic false- reactive overlap between the PRISM assays selected as IA1 and candidate secondary screening immuno- assays (IA2) was calculated to determine the most efficient IA1/IA2 combinations.

RESULTS

There was a significant decrease in the proportion of IA1 RR samples requiring immunoblot testing under the SI strategy when compared with existing site-specific strategies for HIV (0.49 vs. 0.08, p < 0.05), HCV (0.85 vs. 0.42, p < 0.05), and HTLV (0.69 vs. 0.05, p < 0.05) algorithms. In addition, there was a significant decrease in the percentage of immunoblot tests giving indeterminate results for HIV and HTLV under the SI strategy. However, there was no significant difference in the proportion of confirmed positive results for HIV, HCV, or HTLV before and after national SI algorithm implementation. For the anti-HIV IA2s, there was considerable variation of biologic false-reactive overlap with the PRISM HIV O plus chemiluminescent immunoassay (range, 1.6-15.6%).

CONCLUSIONS

The results presented in this report demonstrate that the sequential use of screening immunoassays before immunoblot testing can significantly reduce both the number of immunoblot tests and proportion of indeterminate results, without impacting sensitivity, thereby improving algorithm efficiency and simplifying donor management.

Incidence of seroconversion to positivity for hepatitis C antibody in repeat blood donors in England, 1993-5

OBJECTIVE

To estimate the rate of seroconversion to positivity for hepatitis C antibody in repeat blood donors in England and to describe the probable routes of infection in these donors.

DESIGN

Retrospective survey of blood donors becoming positive for hepatitis C antibody and of the results of donation testing.

SETTING

The 14 blood centres in England.

SUBJECTS

All repeat donors giving blood between January 1993 and December 1995.

MAIN OUTCOME MEASURES

Number of donors developing hepatitis C between donations during the three years of testing for hepatitis C antibody at English blood centres and the rate of seroconversion among repeat blood donors. Probable routes of infection.

RESULTS

14 donors during 1993-5 fulfilled the case definition for seroconversion to positivity for hepatitis C antibody. The estimated seroconversion rate for infection with hepatitis C in repeat donors was 0.26 per 100 000 person years (95% confidence interval 0.15 to 0.43). Counselling after diagnosis found that four of these donors had risk factors specified in the criteria excluding people from giving blood but these factors had not come to light before donation. Another of the donors who seroconverted had a risk factor that has since been included in the exclusion criteria. Heterosexual intercourse was considered to be the most likely route of infection for five of the 14 donors.

CONCLUSIONS

The rate of seroconversion for positivity to hepatitis C antibody in repeat blood donors in England was extremely low. During 1993-5 fewer than 1 in 450 000 donations were estimated to have come from repeat donors who had become positive for hepatitis C antibody since the previous donation.