What dye-binding technique is commonly employed for the quantitation of serum albumin?

Bromocresol Green is the Most Commonly Used Dye-Binding Technique for Serum Albumin Quantitation

Bromocresol green (BCG) is the most commonly employed dye-binding technique for the quantitation of serum albumin in clinical laboratories. 1

Evidence for BCG as the Standard Method

The bromocresol green method has become the predominant technique for measuring serum albumin in clinical settings for several important reasons:

• The BCG colorimetric method is rapid, reproducible, and has been automated, making it ideal for high-volume clinical laboratory use 1
• It uses small aliquots of plasma, has a low coefficient of variation (5.9%), and is not affected by lipemia, salicylates, or bilirubin 1
• Most laboratories utilize the BCG assay as their primary method for measuring serum albumin concentration 1

Comparison with Other Methods

Bromocresol Purple (BCP)

• While BCP is more specific for albumin with specificity similar to electrophoretic methods, it has proved to be clinically less reliable than the BCG method 1
• BCP has been shown to underestimate serum albumin in patients with kidney disease, with a mean difference of 0.71 g/dL in pediatric hemodialysis patients 1
• BCP consistently underestimates albumin values compared to BCG, especially in patients with hypoalbuminemia 2

Other Methods

• Nephelometry and electrophoretic methods are very specific for albumin determination but are time-consuming, expensive, and not generally used in routine clinical laboratories 1
• Biuret method is primarily used for total protein measurement, not specifically for albumin
• Sulfosalicylic acid is used for qualitative protein detection in urine, not for serum albumin quantitation

Clinical Implications of Method Selection

The choice of albumin assay has important clinical implications:

• In patients with nephrotic syndrome, BCG overestimates albumin concentration compared to nephelometry, particularly in severe hypoalbuminemia, due to reaction with α2-macroglobulin 2
• There is a significant difference in albumin values between methods, which affects clinical decision-making:
  • A serum albumin concentration of 25 g/L (2.5 g/dL) with BCG equals approximately 20 g/L (2.0 g/dL) with BCP 1
  • This difference is critical when using albumin levels for risk assessment, such as for thrombotic events in patients with membranous nephropathy 1

Practical Considerations

• The normal range for serum albumin by the BCG method is 3.8 to 5.1 g/dL 1
• When comparing albumin values between laboratories, it's essential to know which method was used
• A conversion formula has been developed: Alb(BCG) = 5.5 + Alb(BCP) 3
• Chronic dialysis units should request the BCG method when available; if BCP must be used, the laboratory's normal range should serve as the reference 1

Potential Pitfalls

• BCG method underestimates albumin in the high normal range and overestimates albumin below the normal range with an overall mean overestimation of approximately 0.61 g/dL 1
• The BCG method is affected by α1- and α2-globulins, which are elevated in systemic inflammation and nephrotic syndrome 2, 4
• When using albumin values for clinical decision-making (such as for anticoagulation in nephrotic syndrome), the method used must be considered 1

In conclusion, while each method has its advantages and limitations, bromocresol green remains the most commonly employed dye-binding technique for serum albumin quantitation in clinical laboratories due to its practicality, speed, and widespread availability.