• Clinical science

Protein analysis

Abstract

Protein in the serum is made up of albumin (∼ 60%) and globulin. Globulin is made up of alpha-1, alpha-2, beta, and gamma globulins. Although a total serum protein measures the total concentration of protein in the serum, it explains very little about the pathological etiology. Serum electrophoresis is an important diagnostic tool for the analysis of individual protein fractions which yields important information about underlying pathologies.

Basics of protein analysis

  • Protein in the serum is made up of albumin (∼ 60%) and globulin. Globulin is made up of alpha-1, alpha-2, beta, and gamma globulins.
  • A total serum protein; (reference range 6–7.8 g/dL) test estimates the total of all protein fractions together, e.g. Biuret test
    • Albumin: 3.5–5.7 g/dL (35–57 g/L)
    • Globulin
      • alpha-1: 0.1–0.4 g/dL (1-4 g/L)
      • alpha-2: 0.3–0.9 g/dL (3–9 g/L)
      • beta: 0.7–1.5 g/dL (7–15 g/L)
      • gamma: 0.5–1.4 g/dL (5–14 g/L)
  • If the result is not within the reference range, one of the following tests is usually performed for further analysis:

References:[1][2][3]

Serum protein electrophoresis

  • Definition: laboratory method to separate proteins and their fragments according to size and electrical charge.
  • After staining and visualization of the results, characteristic patterns associated with certain pathologies become visible.
  • Different electrophoresis procedures serve different purposes. For example, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is a common technique that allows for the separation of proteins based on size alone.

Indications

Procedure

  1. Load serum sample into agarose gel and apply an electrical current
  2. Proteins migrate through the gel
  3. Any proteins with similar properties (size, charge) will accumulate and form bands, regardless of their individual functions
  4. These bands are stained, enabling them to be analyzed and visualized under UV light and charted in an absorption curve. The proteins are separated into one of five major groups (so-called fractions)
  5. The relative quantity of certain proteins can be determined by calculating the area under the curve.
  6. Absolute concentrations of serum proteins can be calculated by multiplying the percentage of a respective fraction by the total serum protein concentration.

Analysis

Name of protein fraction

Albumin

Alpha-1 globulins Alpha-2 globulins Beta globulins Gamma globulins
Fraction contains
Increased in
Decreased in
  • Reduced hepatic synthesis (e.g., cirrhosis)
  • Impaired protein uptake (e.g., malnutrition)
  • Protein loss (e.g., nephrotic syndrome, protein-losing enteropathy, hemorrhage)
  • Severe burns
  • Alpha-1 antitrypsin deficiency
  • Liver disease
  • Malnutrition
  • Agammaglobulinemia
  • Hypogammaglobulinemia

References:[2][4][5][6][7][8][9][10][11][12]