Cold activation of complement enhancing with the duration of storage in sera from blood donors with hepatitis C virus RNA

The cold activation of complement, determined by hemolytic activity of sera stored at low temperature, closely correlates with ongoing hepatitis C virus (HCV) injection. Of 53 189 blood units donated at a blood center in Japan, 187 (0.35%) were positive for antibody to HCV of which 65 (35% of the units with antibody) contained detectable HCV RNA. While sera from the 65 units with HCV RNA had been stored at 4°C, the cold activation of complement was observed in 43 (66%) at day 1, an additional 13 (20%) at day 4, and further in 4 (6%) at day 7. Thus, the cold activation was observed in 60 (92%) of 65 sera with HCV RNA during the storage at low temperature for 7 days. Cryoglobulins were detected only in 13 of the 43 sera which showed the cold activation at day 1, and the donors with cryoglobulinemia were older than the 52 viremic donors without it (mean ± S.D.: 47 ± 10 vs. 40 ± 11 years, P < 0.05). There were no differences in the distribution of HCV genotypes in sera which showed the cold activation at day 1; they were 24 (69%) of 35 sera with genotype $\text{II}\text{1b}$, 15 (68%) of 22 with $\text{III}\text{2a}$ and 4 (50%) of 8 with $\text{IV}\text{2b}$. The results indicate that it would take up to a week before the cold activation is fully manifested in sera from persons infected with HCV.