Abstract
The Japanese Red Cross Blood Services archives donor blood samples from all donations for look-back surveys. These samples, approximately 5 million per year, are stored frozen at –30°C for 11 years and are subsequently discarded. Because such samples may also be valuable for antibody-related research and other purposes after the mandated storage period, we evaluated their potential applicability, with a particular focus on the preservation of anti- body levels. Fresh samples were compared with frozen-stored samples (–30°C for 14 years: 11 years of mandatory good manufacturing practice storage period + 3 years until measurement) for immunoglobulin levels (IgM, IgG, IgA, and IgE) as a general indicator of humoral immunity, tetanus toxin antibody titers as a long-lived vaccine-induced antibody, and ABO antibody titers (saline-direct agglutination test and saline-indirect antiglobulin test [saline-IAT]), which are factors in blood group typing and hemolytic transfusion reactions. For immunoglobulin levels, comparisons of non-paired fresh and frozen-stored samples were made from a random donor population (IgM, IgG, IgA: 105 cases each, IgE: 32 cases). For tetanus toxin antibody and ABO antibody, comparisons were conducted from the same donors with fresh and frozen-stored samples (tetanus toxin antibody: 47 cases, ABO antibody: 12 cases). No significant differences were observed in immunoglobulin levels, tetanus toxin antibody titers, or ABO antibody titers measured by the saline-direct agglutination method. Saline-IAT–measured ABO antibody titers were significantly lower in frozen-stored samples. Detailed results were as follows: (1) Median immunoglobulin levels (fresh vs. frozen-stored): IgM, 78.5 mg/dL versus 86.7 mg/dL; IgG, 1240.2 mg/dL versus 1280.2 mg/dL; IgA, 241.0 mg/dL versus 245.3 mg/dL; and IgE, 0.24 μg/mL versus 0.12 μg/mL. (2) Tetanus toxin antibody titers—geometric mean titer (GMT) (95% confidence interval [CI]): fresh 0.23 (0.12–0.43) IU/mL versus frozen-stored 0.28 (0.17–0.46) IU/mL. (3) ABO antibody titers—GMT (95% CI): saline-direct agglutination, fresh 65.4 (33.3–128.5) versus frozen-stored 51.7 (24.9–107.4); saline-IAT, fresh 391.0 (160.3–953.6) versus frozen-stored 248.7 (107.8–573.6). The evaluated immunoglobulin levels were largely preserved, suggesting that archived blood samples retain sufficient stability for antibody research. However, careful study design is necessary to minimize potential sample deterioration.