Exposure of blood plasma/serum (P/S) to thawed conditions (> -30 °C) can produce biomolecular changes that skew measurements of biomarkers within archived patient samples, potentially rendering them unfit for molecular analysis. Since freeze-thaw histories are often poorly documented, objective methods for assessing molecular fitness prior to analysis are needed.
This presentation will described the concept, methodology, validation and performance characteristics of a 10-µL, dilute-and-shoot, intact-protein mass spectrometric assay of albumin proteoforms called “Delta-S-Cys-Albumin” that serves as an endogenous marker of P/S exposure to thawed conditions based on the inexorable ex vivo S-cysteinylation (oxidizability) of albumin. The multi-reaction chemical mechanism that drives changes in albumin S-cysteinylation is known and the rate law for it was established and accurately modeled in P/S—enabling back-calculation of the time at which unknown P/S specimens have been exposed to the equivalent of room temperature. Results from blind challenges and two unanticipated case studies that revealed unexpected integrity problems in sets of nominally pristine P/S samples will be presented.