Serum albumin

Introduction

• Serum Albumin Test is a commonly performed laboratory test used to measure the concentration of albumin in blood serum.

• Albumin is the most abundant protein present in human plasma and plays an important role in maintaining normal physiological functions.

• It helps in maintaining osmotic pressure and fluid balance between blood vessels and body tissues.

• Albumin also acts as a transport protein, carrying hormones, fatty acids, drugs, vitamins, and other substances in the bloodstream.

• The Serum Albumin Test is widely used in clinical laboratories for evaluating liver function, since albumin is synthesized in the liver.

• It is also helpful in the diagnosis and monitoring of kidney diseases, especially conditions causing protein loss in urine.

• Measurement of albumin levels can indicate nutritional status and protein deficiency in patients.

• Quantitative estimation of serum albumin is commonly performed using automated biochemical analyzers or photometric methods in clinical biochemistry laboratories.

 

---

Principle

---

• Albumin binds with Bromocresol Green dye at acidic pH (around 4.2).

• This reaction forms a blue-green colored complex.

• The intensity of the color produced is proportional to the concentration of albumin in the sample.

• The absorbance is measured photometrically between 540–630 nm, with maximum absorbance near 625 nm.

 

---

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.

 

---

Specimen Collection

---

Sample Type

• Serum

• Plasma (EDTA or heparinized plasma)

Precautions

• Avoid hemolysed samples

• Follow proper sample collection techniques

• Discard contaminated samples

Sample Stability

• Stable for 1 month at 2–8°C

• Stable for 1 week at room temperature

• Stable for up to 3 months at –20°C

 

---

Requirements

---

1. 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.
2. Reagents:
   • Bromocresol green (BCG) dye reagent.
   • Buffer solution (pH 4.0–4.2).
   • Distilled water.
3. Equipment:
   • Spectrophotometer or colorimeter.
   • Pipettes and cuvettes.

 

---

Procedure (Using the Bromocresol Green Method)

---

1. Preparation of Reagents:
   • Prepare the BCG dye solution as per the manufacturer’s instructions.
2. Sample Preparation:
   • Obtain serum from a centrifuged blood sample.
3. Reaction Setup:
   • Label test tubes for blank, standard, and test samples.
   • Add the following:

Component	Blank	Standard	Test Sample
BCG Reagent	1 mL	1 mL	1 mL
Serum Sample	—	—	20 µL
Standard Albumin	—	20 µL	—
DH2O	20 µL	—	—

1. Incubation:
   • Mix well and incubate at room temperature for 10 minutes.
2. 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:

1. • 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

---

Increased Albumin Levels

High albumin levels may be seen in:

• Dehydration

• Hemoconcentration due to venous stasis during blood collection

Decreased Albumin Levels

Low albumin levels may occur in:

• • Liver diseases

  • Kidney diseases with protein loss

  • Malnutrition

  • Malabsorption syndromes

  • Protein-losing enteropathy

  • Severe burns or skin diseases

  • Chronic infections or fever

  • Uncontrolled diabetes mellitus

  • Hypertension