Assessment of the quality of frozen serum by spectrophotometric analysis and sperm bioassay

Serum is an integral part of media used for in vitro fertilization (IVF) and andrology work. Previous studies showed that the IVF results could benefit if sera were screened for deleterious effects before use. Such screening is impractical when fresh sere are used but may be feasible if the serum is frozen prior to use. This study assessed the impact of freezing on the quality of serum. A total of 158 serum samples, prepared in a university- based andrology-IVF center, were included in the study. The frozen sere were thawed in hatches to be used in a series of laboratory experiments. Serum quality was evaluated by spectrophotometric analysis and sperm bioassay under several defined conditions: fresh, frozen, pre- and postfiltration, pre- and postcentrifugation, and the patients' fertility condition. Although all sera were filtered through 0.22-μm filter, more than 10% frozen sere required 0.4- or a combination of 0.8- and 0.4-μm filters before they could be passed through the 0.22-μm filter. Frozen sera that were directly filtrable with a 0.22-μm filter lost 13% turbidity upon filtration. The turbidity of the frozen sera were higher compared to fresh ones as revealed by optical density (OD) and relative light scattering (RLS) spectrophotometry. The freeze/storage-induced spectrophotometric changes did not correlate with the storage time. The centrifugation caused precipitation of sere components. The rate of precipitation of the serum components correlated with the duration of freezing. Spectrophotometric analysis and sperm bioassay did not differentiate the sera of pregnancypositive and pregnancy-negative subjects. The sperm bioassay failed to detect any biological impact of freezing- induced spectrophotometric changes in the sere, suggesting that the freezing- induced changes did not significantly diminish the serum's capability of supplementing the culture media.