Comparison of Urine and Plasma Biomarker Concentrations Measured by Aptamer-Based versus Immunoassay Methods in Cardiac Surgery Patients

Background: Protein detection assays are invaluable tools in the field of biomarker discovery. However, only immunoassays are widely used and can measure 10-20 analytes per biosample. The novel SOMAmer-based assay uses nucleotide aptamer technology to measure over 1300 analytes per biosample. We compared the SOMAmer-based platform to traditional approaches to quantify analytes in a clinical setting with paired samples before and after cardiac surgery. Methods: In a substudy of the Translational Research Investigating Biomarker Endpoints in Acute Kidney Injury cohort, 54 individuals with acute kidney injury after cardiac surgery were identified. Preoperative and postoperative plasma and urine samples that had been previously evaluated for biomarker concentrations via immunoassays were analyzed via SOMAmerbased assay. Results: Spearman correlations were estimated when >50% of biomarker values were within detectable ranges by immunoassay (plasma biomarkers: preoperative, 26/33; postoperative, 31/33; urine biomarkers: preoperative, 13/16; postoperative, 16/16). Overall, 27% of reportable plasma preoperative biomarkers displayed correlations =0.75 between immunoassay and SOMAmer measurements; 23% displayed correlations of 0.50 - 0.75, and 50% displayed correlations <0.50. In urine these values were 15%, 39%, and 46%, respectively. Forty-two percent of reportable plasma postoperative biomarkers displayed correlations =0.75, 16% displayed correlations 0.50 - 0.75, and 42% displayed correlations < 0.50. In urine, these values were 19%, 25%, and 56%, respectively. Conclusions: In cardiac surgery patients, the SOMAmer-based assay detects proteins with moderate to strong correlation to current immunoassay methods. The correlations in urine are weaker than those in plasma. SOMAmer-based assay technology should be further evaluated in multiple settings as a high-throughput screening tool for biomarker discovery.