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 (IV F) and andrology work. Previous studies showed that the IVF results co uld benefit if sera were screened for deleterious effects before use. Such screening is impractical when fresh sera are used but may be feas ible if the serum is frozen prior to use. This study assessed the impa ct 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 sera were thawed in batches to be used in a seri es of laboratory experiments. Serum quality was evaluated by spectroph otometric analysis and sperm bioassay under several defined conditions : fresh, frozen, pre-and postfiltration, pre-and postcentrifugation, a nd the patients' fertility condition. Although all sera were filtered through 0.22-mu m filter, more than 10% frozen sera required 0.4- or a combination of 0.8- and 0.4-mu m filters before they could be passed through the 0.22-mu m filter. Frozen sera that were directly filtrable with a 0.22-mu m filter lost 13% turbidity upon filtration. The turbi dity of the frozen sera were higher compared to fresh ones as revealed by optical density (OD) and relative light scattering (RLS) spectroph otometry. The freeze/storage-induced spectrophotometric changes did no t correlate with the storage time. The centrifugation caused precipita tion of sera components. The rate of precipitation of the serum compon ents correlated with the duration of freezing. Spectrophotometric anal ysis and sperm bioassay did not differentiate the sera of pregnancy-po sitive and pregnancy-negative subjects. The sperm bioassay failed to d etect any biological impact of freezing-induced spectrophotometric cha nges in the sera, suggesting that the freezing-induced changes did not significantly diminish the serum's capability of supplementing the cu lture media.