Introduction
- Serum albumin is the most abundant protein in human plasma, synthesized primarily by the liver.
- It plays a critical role in maintaining oncotic pressure and serves as a carrier for various substances, including hormones, drugs, and fatty acids.
- Measuring serum albumin is essential in evaluating liver function, nutritional status, and the presence of certain medical conditions such as nephrotic syndrome and chronic infections.
Principal
The determination of serum albumin typically relies on its ability to bind to specific dyes, such as bromocresol green (BCG) or bromocresol purple (BCP), which produce a color change proportional to the albumin concentration. The intensity of the color can be measured photometrically, providing a quantitative result.
Method
- Dye-binding method (most common): Albumin binds to a dye, producing a measurable color change.
- Immunoassay: Albumin is detected using specific antibodies.
- Electrophoresis: Separates albumin from other plasma proteins for quantification.
The bromocresol green (BCG) method is widely used due to its simplicity and reliability in routine clinical settings.
Requirements
- Sample:
- Serum or plasma (collected in a heparinized or EDTA tube). Hemolysis should be avoided as it may interfere with results.
- Volume: 0.5–1 mL of serum/plasma.
- Reagents:
- Bromocresol green (BCG) dye reagent.
- Buffer solution (pH 4.0–4.2).
- Distilled water.
- Equipment:
- Spectrophotometer or colorimeter.
- Pipettes and cuvettes.
Procedure (Using the Bromocresol Green Method)
- Preparation of Reagents:
- Prepare the BCG dye solution as per the manufacturer’s instructions.
- Sample Preparation:
- Obtain serum from a centrifuged blood sample.
- Reaction Setup:
- Label test tubes for blank, standard, and test samples.
- Add the following:
| Component | Blank | Standard | Test Sample |
| Buffer Solution | 1 mL | 1 mL | 1 mL |
| BCG Reagent | 1 mL | 1 mL | 1 mL |
| Standard Albumin | — | 20 µL | — |
| Serum Sample | — | — | 20 µL |
- Incubation:
- Mix well and incubate at room temperature for 10 minutes.
- Measurement:
- Measure the absorbance at 630 nm using a spectrophotometer.
Calculation
Formula:
Albumin concentration (g/dL) = (Absorbance of test/Absorbance of standard) × Concentration of standard
Example:
-
- Absorbance of test = 0.45
- Absorbance of standard = 0.50
- Concentration of standard = 4.0 g/dL
- Calculation: Albumin = (0.45/0.50)×4.0=3.6 g/dL
Normal Values
- Adults: 3.5–5.0 g/dL
- Children: 3.8–5.4 g/dL
- Newborns: 3.0–4.5 g/dL
Clinical Significance
- Low Albumin Levels (Hypoalbuminemia):
- Liver disease: Cirrhosis, hepatitis.
- Kidney disease: Nephrotic syndrome, proteinuria.
- Malnutrition: Protein-energy malnutrition.
- Chronic illnesses: Infections, inflammation, cancer.
- High Albumin Levels (Hyperalbuminemia):
- Rare; may occur due to dehydration or over-replacement during intravenous therapy.