The bromocresol green assay, but not the modified bromocresol purple assay, overestimates the serum albumin concentration in nephrotic syndrome through reaction with α2-macroglobulin.

Abstract

BACKGROUND:

The bromocresol green (BCG) assay is commonly used for measuring albumin (ALB), but is affected by α1- and α2-globulins, which are elevated in systemic inflammation. The modified bromocresol purple (mBCP) assay is another dye-binding method developed to overcome non-specific reactions. Concentrations of α2-macroglobulin, a major α2-globulin component, are increased in nephrotic syndrome (NS), but not in inflammation. There is little direct evidence that α2-macroglobulin affects BCG or mBCP assays.

METHODS:

We measured serum albumin concentrations in 33 patients with NS and 13 reference healthy controls using BCG (ALBBCG) and mBCP (ALBmBCP) assays, and nephelometry (nALB) as a reference method. We also determined five specific proteins belonging to the α1- and α2-globulins by nephelometry. After adding purified α2-macroglobulin to albumin solutions, protein reactivity in these three assays was compared.

RESULTS:

Nephrotic syndrome patients were categorized to tertiles according to nALB concentration. In all tertiles, ALBBCG was significantly higher than nALB, especially in the severe hypoalbuminemia group, in which α2-macroglobulin was 43-49% higher. By contrast, ALBmBCP and nALB were almost identical in all three groups. The difference between ALBBCG and nALB was positively correlated with the α2-macroglobulin concentration. In vitro, when α2-macroglobulin was added to solutions containing identical albumin concentrations, α2-macroglobulin dose-dependently increased ALBBCG, but not ALBmBCP.

CONCLUSIONS:

In NS, α2-macroglobulin is a major factor for positive bias of ALBBCG, especially in patients with severe hypoalbuminemia. The mBCP assay is useful for measuring albumin concentrations in NS.

• Authors: Tsuyoshi Ueno, Satoshi Hirayama, Masami Sugihara, Takashi Miida
• Journal: Annals of clinical biochemistry (Ann Clin Biochem) Vol. 53 Issue Pt 1 Pg. 97-105 (Jan 2016) ISSN: 1758-1001 [Electronic] England
• PMID: 25673775 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © The Author(s) 2015.

Chemical References

• Serum Albumin
• alpha-Macroglobulins
• Bromcresol Purple
• Bromcresol Green

Topics

• Blood Chemical Analysis (methods)
• Bromcresol Green (chemistry)
• Bromcresol Purple (chemistry)
• False Positive Reactions
• Female
• Humans
• Male
• Middle Aged
• Nephrotic Syndrome (blood)
• Serum Albumin (analysis, chemistry)
• alpha-Macroglobulins (analysis)