Effect of Long-Term Freezing on Indirect Fluorescent Antibody Titers for the Diagnosis of Equine Protozoal Myeloencephalitis.
Authors: Valderrama-Martinez Claudia, Packham Andrea, Smith Woutrina, Mendoza-Flores Jorge Eduardo, Zheng Shichen, Chigerwe Munashe, Plancarte Magdalena, Aleman Monica
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Long-Term Storage Effects on EPM Antibody Testing Diagnosis of equine protozoal myeloencephalitis relies heavily on indirect fluorescent antibody testing of serum and cerebrospinal fluid, with interpretation often guided by serum-to-CSF antibody ratios; however, the stability of these samples during prolonged frozen storage—common in research settings and diagnostic workflows—has remained largely unexplored. Researchers evaluated 71 paired and serum-only equine samples stored at -80°C across three timeframes (6–12, 13–18, and 19–24 months), comparing antibody titers against *Sarcocystis neurona* and *Neospora hughesi* between initial testing and repeat testing after extended freezing. Whilst *S. neurona* antibodies proved relatively stable across all storage periods, *N. hughesi* antibody detection in CSF showed statistically significant degradation after 19–24 months (p = 0.04); more concerning clinically, the diagnostic serum-to-CSF ratio interpretation shifted in 41% of paired samples, potentially altering case assessment despite individual antibody values appearing relatively unchanged. These findings suggest that laboratories and practitioners should exercise caution when interpreting EPM test results from samples frozen beyond 18 months, particularly when relying on serum-to-CSF ratios for disease confirmation, and that archives of frozen diagnostic or research samples may require retesting rather than reliance on historical results.
Read the full abstract on PubMed
Practical Takeaways
- •CSF samples stored longer than 18 months should be recollected and re-tested rather than relying on frozen samples, particularly for N. hughesi antibody testing in diagnostic work-ups for EPM
- •When evaluating historical serum-to-CSF antibody ratios for EPM diagnosis, consider sample storage duration; changes in ratio interpretation occurred in 41% of samples stored 19-24 months, which could alter clinical conclusions
- •For research purposes, establish baseline fresh-sample testing protocols and plan sample collection accordingly, as freeze-storage beyond 18 months introduces variables that compromise diagnostic accuracy
Key Findings
- •N. hughesi IFAT results in CSF were significantly altered after 19-24 months of -80°C storage (p=0.04), but serum samples were not significantly affected
- •No statistical differences were observed for S. neurona IFAT in serum or CSF samples across all storage periods (6-24 months)
- •Serum to CSF ratio cutoff interpretation changed in 41% (19 of 46) of paired samples, potentially altering clinical diagnosis classification
- •Long-term freezing storage beyond 18 months at -80°C may compromise test result reliability and affect disease diagnosis interpretation