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Proteomics and Protein Markers |
Departments of1 Laboratory Medicine and 2 Critical Care Medicine, Warren Magnuson Clinical Center, National Institutes of Health, Bethesda, MD.
aAddress correspondence to this author at: Department of Laboratory Medicine, National Institutes of Health, Building 10, Room 2C-407, Bethesda, MD 20892-1508. Fax 301-402-1885; e-mail ghortin{at}mail.cc.nih.gov.
Background: Size-exclusion HPLC has been used as an alternative to immunoassays for quantifying urinary albumin (microalbumin). Systematically higher values for the HPLC method have been proposed to result from nonimmunoreactive albumin.
Methods: We evaluated separation of purified proteins and urinary components by size-exclusion HPLC using a Zorbax Bio Series GF-250 column eluted with phosphate-buffered saline. Urinary components eluting in the "albumin" peak were analyzed by mass spectrometry and reversed-phase HPLC.
Results: Several proteins, such as transferrin,
1-proteinase inhibitor,
1-acid glycoprotein, and
2-HS glycoprotein, analyzed as purified components, were not resolved from albumin by size-exclusion HPLC. Peaks for other proteins, such as IgG and urinary components identified as dimers of
1-microglobulin and immunoglobulin light chains, overlapped with the albumin peak. Profiles of urine specimens showed variable amounts of components overlapping with albumin. Furthermore, the albumin peak obtained by size-exclusion HPLC was found by mass spectrometry and reversed-phase HPLC to contain multiple components in addition to albumin.
Conclusions: Size-exclusion HPLC does not resolve albumin from several other proteins in urine. The albumin peak resolved by this technique, although predominantly composed of albumin, contains several coeluting globulins that would contribute to overestimation of albumin concentration by size-exclusion HPLC.
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