The significance of third-generation HCV RIBA-indeterminate, RNA-negative results in voluntary blood donors screened with sequential third-generation immunoassays.
BACKGROUND
One of the problems associated with the use of anti-HCV immunoblot assays is the interpretation of indeterminate results without detectable HCV RNA. The purpose of this study was to examine the significance of third-generation RIBA (RIBA-3)-indeterminate, RNA-negative results in voluntary blood donors.


METHODS
Since June 2000 all Australian Red Cross Blood Service testing sites have used an anti-HCV sequential immunoassay testing strategy whereby donors who are reactive on the primary screening immunoassay are tested on a secondary immunoassay and if reactive on both assays, further tested by immunoblot. From the four testing sites that use RIBA-3, the result profiles of donors who were RIBA-3-indeterminate, HCV RNA-negative were analyzed.


RESULTS
From 2,661,786 donations screened for anti-HCV during the study period, 102 RIBA-3-indeterminate, RNA-negative donors were identified, most of whom were reactive to either c33p (69.6%) or c22p (27.5%). The RIBA-3-indeterminate, RNA-negative donors showed a significantly higher screening immunoassay signal strength to assay cutoff (S/CO) distribution than those with biologic false-reactive (BFR) results (1.853 vs. 1.524, p < 0.05) but a significantly lower distribution than RIBA-3-positive, RNA-negative (1.853 vs. 4.546, p < 0.05) or RNA-positive (1.853 vs. 6.467, p < 0.05) donors. The RIBA-3-indeterminate, RNA-negative donors showed a similar distribution of c33c and c22p band intensities compared with RIBA-3-positive, RNA-negative donors but significantly lower distribution of band strengths compared to the RIBA-3-positive, RNA-positive group. Compared to the indeterminate donors with previous anti-HCV-negative or BFR results, the indeterminate donors not previously screened for anti-HCV showed higher immunoassay S/CO ratio distributions, a higher proportion with c22p reactivity (16.2% vs. 36.7%), and higher frequency of risk factors (46.4% vs. 75.0%).


CONCLUSIONS
Our analysis suggests that a combination of indicators can be used to help clarify RIBA-3-indeterminate, RNA-negative results. Specifically, donors with high S/CO ratios on a screening immunoassay, RIBA-3 reactivity to c22p or c33c with band intensity of 2+ or greater, without a previous history of negative or BFR donations and with an identifiable risk factor, have a high probability of representing true anti-HCV rather than nonspecific reactivity.
Virus Serology Laboratory, Australian Red Cross Blood Service-Victoria, PO Box 354, South Melbourne, Victoria 3205, Australia. pkiely@arcbs.redcross.org.au
Philip
P
Kiely
Deborah
D
Kay
Susan
S
Parker
Lisa
L
Piscitelli
D000094902:Blood Banking / Q000379:methods; D001782:Blood Donors; D016174:Hepacivirus / Q000235:genetics / Q000302:isolation & purification*; D006526:Hepatitis C / Q000175:diagnosis* / Q000453:epidemiology; D006801:Humans; D007118:Immunoassay; D008403:Mass Screening; D012367:RNA, Viral / Q000032:analysis; D012307:Risk Factors
D012367:RNA, Viral