Sandwich enzyme-linked immunosorbent assay for the quantification of human serum albumin fragment 408–423 in bodily fluids

Evaluation of EPI-X4 as a urinary peptide biomarker for diagnosis and prognosis of late acute GvHD

“…Frozen urine aliquots were rapidly thawed and immediately analyzed using an EPI-X4 specific sandwich ELISA. 7,10 . This validated ELISA is highly specific for EPI-X4 as it does not cross-react with other albumin fragments or the albumin precursor.…”

“…Furthermore, it has a low intra-assay variation, a linear range between 0.078 and 5 ng/ml, and a limit of detection for EPI-X4 in urine of ~ 0.154 ng/ml. 10 …”

“…Multivariate analyses were planned but not conducted because of the limited number of patients with positive values. It is unlikely that external factors such as sample processing or technical problems with the ELISA affected our results because EPI-X4 is stable for 24 hours at room temperature in urine and through multiple freeze-thaws 10 . The urine samples used in this study were frozen without processing unless they were obviously turbid, in which case they were first centrifuged.…”

“…Neither processing method affects EPI-X4 levels. 7,10 Finally, the positive controls for each run were detected at appropriate levels and there were no technical difficulties with the assay. In summary, our results suggest that urinary levels of EPI-X4 are for the most part not detectable by ELISA in the patients we studied.…”

“…These values are more than four orders of magnitude higher than the detection limit of the ELISA. 10 …”