ORTHO® HCV, Version 3.0 ELISA Test System
The specificity of ORTHO HCV Version 3.0 ELISA Test System in low-risk populations is based on a population of blood donors from four different test sites. A total of 33,025 specimens were tested. These consisted of 30,025 specimens from presumably healthy volunteer blood donors (sites 1, 2 and 3) and 3,000 specimens from commercial plasma donors (site 4). Rates of initial and repeat reactivities are shown in the table below. Correlation between initial and repeat reactivity was 87.1%.
| Prevalence of Anti-HCV Reactivity in Blood Donors |
| Site | Number Tested | Nonreactive | Initially Reactive | Repeatedly Reactive |
| 1 | 10,208 | 10,169 | 47 (0.46%) | 39 (0.38%) |
| 2 | 9,772 | 9,722 | 54 (0.55%) | 50 (0.51%) |
| 3 | 10,045 | 9,998 | 54 (0.54%) | 47 (0.47%) |
| 4 | 3,000 | 2,987 | 16 (0.53%) | 13 (0.43%) |
| Total | 33,025 | 32,876 | 171 (0.52%) | 149 (0.45%) |
Specimens repeatedly reactive by ELISA were tested by supplemental strip immunoblot assay (SIA). Upon removal of specimens that were positive or indeterminate by SIA, specificity* in this low prevalence population was 99.95% (5 units per 10,000 donations).
*Specificity was calculated as follows: Specificity = (TN/TN+FP)
- Where TN = true negatives, that is, the number of specimens nonreactive by ELISA.
- Where FP=false positives, that is, repeatedly reactive by ELISA and negative by SIA.
