Stability of immunoglobulin E (IgE) in stored obstetric sera

Objective: To determine the stability of immunoglobulin E levels in obstetric sera. Methods: AlaSTAT(R) and AlaTOP(R) (Diagnostic Products) were used to assay total and specific IgE levels in obstetric sera collected in Memphis, TN and Portland, OR. The samples were collected from the Collaborative Perinatal Project (CPP) between 1959 and 1965 and stored at - 20°C. The assay results were compared with IgE levels found in sera collected at the same locations for the Calcium for Pre-eclampsia Prevention Study (CPEP) and stored since 1992 at -70°C. The samples were also assayed for cockroach (CR) and mouse urine specific IgE using the AlaSTAT(R) assay (Diagnostic Products). Results: Total IgE and specific IgE to CR and mouse urine were detectable in older and recent samples. The median total IgE for the recent and older Portland samples was 26 IU/ml and 65 IU/ml, respectively. The median total IgE was identical (40 IU/ml) in the recent and older Memphis samples. Conclusion: Long-term storage does not diminish the ability to measure serum IgE. Levels of IgE in sera stored 32-37 years were equal to or greater than levels in sera stored for 5 years.