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The Bromocresol Green Assay, but Not the Modified Bromocresol Purple Assay, Overestimates the Serum Albumin Concentration in Nephrotic Syndrome Through Reaction With α2-macroglobulin

The Bromocresol Green Assay, but Not the Modified Bromocresol Purple Assay, Overestimates the Serum Albumin Concentration in Nephrotic Syndrome Through Reaction With α2-macroglobulin

Tsuyoshi Ueno, Satoshi Hirayama, Masami Sugihara, Takashi Miida

Ann Clin Biochem. 2016 Jan;53(Pt 1):97-105.

PMID: 25673775

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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP115402	Bromocresol Purple		115-40-2	Price

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