Measurement of glycated albumin in serum and plasma by LC-MS/MS

Background Diagnosis of diabetes and monitoring of long-term blood sugar are preferably done by measurement of glycated hemoglobin (HbA1c). Diabetic patients with end stage renal disease (ESRD) may have short-lived red blood cells due to hemodialysis (HD), and thus higher turnover of hemoglobin. The level of glycated hemoglobin (HbA1c) may be lower than expected for these patients, even at increased blood glucose, possibly making glycated albumin (GA) measurement a better alternative. Methods The percentage of GA was measured by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Fast and efficient trypsin digestion of proteins in diluted serum or plasma resulted in a high number of proteotypic peptides from albumin, including KQTALVELVK which was detected both glycated and non-glycated by multiple reaction monitoring (MRM). The percentage of GA was estimated by neat peak area response of glycated peptide divided by the sum of glycated and non-glycated peptide. Results Acceptable method reproducibility (6% CV), repeatability (2-6% CV), limit of quantification (0.75% GA), linearity (R-2 = 0.999) and recovery (79 +/- 9%) was achieved without using calibration or isotope-labeled internal standard. GA was strongly correlated with HbA1c (r = 0.84) for patients without ESRD. The average ratio of GA/HbA1c was significantly higher (p = 0.0021) for ESRD patients (1.84 +/- 0.38, n = 62) compared to other patients (1.67 +/- 0.28, n = 225). Conclusion GA measurement by detecting glycation in KQTALVELVK with LC-MS/MS seems to be a useful supplement to HbA1c for detecting increased blood glucose in diabetic patients with ESRD.