Long-term sera storage does not significantly modify the interpretation of toxoplasmosis serologies

- Laboratory Quality Assurance requires proof of sera validity after long-term storage.
- Anti-Toxoplasma IgG and IgM are stable in time when frozen at − 20 °C.
- Slight changes after storage are mainly due to intrinsic serological variability.
- Clinical and immunological factors do not impact immunoglobulins stability.
- Sera provide valid toxoplasmosis serological results for up to 7 years of storage.

BackgroundSerological investigation of Toxoplasma gondii can answer many questions about toxoplasmosis in human pathology. Along these lines, studies on serum storage in biobanks need to be performed especially in terms of determining the impact of storage on relevance of sera analysis after freezing. This study assessed the impact of long-term sera storage on the stability of anti-Toxoplasma immunoglobulins.Material and methodsThe stability of anti-Toxoplasma IgG and IgM was studied in 244 and 242 sera respectively, stored at − 20 °C from one month to ten years. ELISA-immunoassay (Vidas®, bioMérieux) was used for initial and post-storage analyses. Linear models for repeated measures and subgroup analyses were performed to assess the effect of storage duration and sample characteristics on immunoglobulins stability.ResultsUntil ten years, the variability attributed to storage (maximum 8.07% for IgG, 13.17% for IgM) was below the variations inherent to the serological technique and allowed by quality assurance systems (15%). Subgroup analysis reported no variation attributed to sera storage. Serological interpretation was modified for 3 sera (1.2%) tested for IgM, all stored more than seven years.ConclusionAnti-Toxoplasma immunoglobulins can reliably be measured for at least up to six years of storage with no modification of interpretation of toxoplasmosis serologies.