HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: clinchem.2007.092825v1 54/1/61    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Sviridov, D. Articles by Hortin, G. L. Search for Related Content PubMed PubMed Citation Articles by Sviridov, D. Articles by Hortin, G. L. Related Collections Proteomics and Protein Markers

Reactivity of Urinary Albumin (Microalbumin) Assays with Fragmented or Modified Albumin

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, NIH, Building 10, Room 2C-407, Bethesda, MD 20892-1508. Fax 301-402-1885; e-mail ghortin{at}mail.cc.nih.gov.

Background: Controversy exists regarding occurrence and measurement of structural variants of albumin in urine. In this study, we examined cross-reactivity of in vitro modified albumins in assays for urine albumin (microalbumin).

Methods: We analyzed albumin modified by reagents, trypsin, or physical treatments or differing in primary sequence (animal albumins) with an immunoturbidimetric assay (Beckman LX20) using goat antiserum and a competitive immunoassay (Siemens Immulite) using a monoclonal antibody. We assessed occurrence of albumin fragments in urine by use of Western blotting of 24 specimens.

Results: Chemical modification, modest sequence substitution (gorilla albumin), or cleavage of albumin by cyanogen bromide (CNBr) had little effect on reactivity in the LX20 assay. Albumin extensively cleaved with trypsin retained partial reactivity. The Immulite assay generally was affected more severely by albumin modifications and sequence changes. Western blots of fresh urine specimens or specimens stored at –80 °C showed little albumin fragmentation, but some specimens stored for 3 years at –20 °C had extensively fragmented albumin that was detected by the LX20 but not the Immulite assay.

Conclusions: Nearly equivalent reactivity of intact albumin and CNBr fragments in the immunoturbidimetric assay indicates reactivity of antibodies with multiple epitopes throughout albumin. Therefore, it is difficult to abolish reactivity of albumin in this type of urine albumin assay. Differential sensitivity of 2 assays to albumin modification identifies a potential source of assay nonequivalence in measuring urinary albumin, particularly for specimens stored at –20 °C.

The following articles in journals at HighWire Press have cited this article:

				J. C. Seegmiller, D. R. Barnidge, B. E. Burns, T. S. Larson, J. C. Lieske, and R. Kumar Quantification of Urinary Albumin by Using Protein Cleavage and LC-MS/MS Clin. Chem., June 1, 2009; 55(6): 1100 - 1107. [Abstract] [Full Text] [PDF]

				E. J Lamb, F. MacKenzie, and P. E Stevens How should proteinuria be detected and measured? Ann Clin Biochem, May 1, 2009; 46(3): 205 - 217. [Abstract] [Full Text] [PDF]

				W. G. Miller, D. E. Bruns, G. L. Hortin, S. Sandberg, K. M. Aakre, M. J. McQueen, Y. Itoh, J. C. Lieske, D. W. Seccombe, G. Jones, et al. Current Issues in Measurement and Reporting of Urinary Albumin Excretion Clin. Chem., January 1, 2009; 55(1): 24 - 38. [Abstract] [Full Text] [PDF]