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Laboratory Six: Total Protein and Albumin Determinations

INTRODUCTION

  • Serum Proteins: Essential for water distribution and acid-base balance between tissues and blood.
  • Types of Serum Proteins: Grouped as albumin and globulins.
  • Clinical Value: Total serum protein determination aids in clinical diagnoses.
  • Additional Tests for Protein Status: Serum albumin, transferrin, prealbumin, and others.

OBJECTIVES

  • Determine total serum protein as part of protein visceral status.
  • Determine serum albumin as another component of protein visceral status.

BACKGROUND

Functions of Proteins

  • Structural Functions: Collagen and elastin.
  • Regulatory Functions: Hormones and enzymes.
  • Carrier Proteins: Transport bilirubin, calcium, lipids, metals, oxygen, steroids, thyroid hormones, and vitamins.
  • Immune Response Mediators: Antibodies.

Protein Distribution

  • Total Protein in Adult Body: 10-13 kg based on a 70 kg male reference.
  • Protein Distribution by Tissue (g/kg):
    • Muscle: 22
    • Skeleton: 20
    • Viscera & Skin: 18
    • Extracellular: 17
    • Adipose Tissue: 6
  • Body Cell Mass:
    • Skeletal Muscle: 30-50% of total body proteins.
    • Visceral Proteins: Serum proteins from erythrocytes, granulocytes, lymphocytes.
    • Solid Tissues: Liver, kidneys, pancreas, heart.

Noncellular Structural Proteins

  • Found in extracellular connective tissue: cartilage, fibrous, and skeletal tissues.

Functions of Serum Proteins

  • Maintain water distribution, acid-base balance, transport, and immunity.

Protein Stores

  • No dispensable protein stores in humans; loss leads to structural element loss and impaired functions.

Protein Quality

  • Animal Proteins: Provide all essential amino acids (except gelatin).
  • Plant Proteins: Incomplete proteins; variety essential for amino acid completeness; soy protein offers a high amino acid score.

Serum Total Protein Concentration

  • Increases In:
    • Dehydration (vomiting/diarrhea), multiple myeloma, nephrotic syndrome, low protein intake/malabsorption, starvation, severe hemorrhage, liver disease.
  • Decreases In:
    • Inadequate protein intake (anorexia, unbalanced diets), altered metabolism (trauma, stress, sepsis, hypoxia).

Specific Deficiency of Plasma Proteins

  • Conditions: Protein-losing enteropathy, liver disease, drug effects, strenuous exercise, inadequate energy intake, electrolyte/trace element deficiencies, vitamin deficiencies, pregnancy.

ASSESSMENT OF PROTEIN STATUS

  • Somatic Protein Methods: Urinary creatinine excretion, creatinine/height ratio, 3-methylhistidine excretion.
  • Visceral Protein Methods: Total serum protein, serum albumin, serum transferrin, prealbumin, retinol-binding protein, C-reactive protein.
    • Total Serum Protein (TP): Not sensitive to protein status; depleted only with clinical signs of malnutrition.
    • Albumin: Negative acute-phase responder; half-life ~20 days; assesses chronic malnutrition/muscle loss.
    • Prealbumin: Negative acute-phase responder; half-life ~2 days; assesses acute changes.

PROTEIN-ENERGY MALNUTRITION (PEM)

  • Definition: Deficiency of both protein and energy (kcal).
  • Marasmus: Absolute food deprivation; results in skeletal muscle depletion; albumin shifts intravascularly.
  • Kwashiorkor: Low protein intake relative to energy; depletion of visceral protein pool; edema; albumin shifts extravascularly.

Reference Values for Protein Analytes

  • Total Protein (TP): 6.5-8.3 g/dL (Low < 6.5, Medium 6-6.4, High < 6.0)
  • Globulin: 2.3-3.5 g/dL;
  • Albumin: 3.5-5.0 g/dL (Mild-to-no risk >3.2 mg/dL, Moderate 2.5-3.2 mg/dL, Severe <2.5 mg/dL)
  • Prealbumin: 19-43 mg/dL (Mild-to-no risk >17 mg/dL, Moderate 10-17 mg/dL, Severe <10 mg/dL)
  • Transferrin: 212-360 mg/dL (Mild 150-200 mg/dL, Moderate 100-150 mg/dL, Severe <100 mg/dL)
  • Creatinine: 0.6-1.5 mg/dL

PROCEDURES

A. Total Protein (TP)

  • Principle: Biuret reaction; formation of colored complex with copper ions in alkaline solution. Violet color at 550 nm is proportional to total protein concentration.
  • Specimen: Serum (not plasma due to fibrinogen).

B. Serum/Plasma Albumin

  • Principle: Dye binding technique using bromocresol green; color intensity at 550 nm correlates with albumin concentration.
  • Specimen: Serum or plasma (EDTA/heparin).

QUESTIONS

  1. Explain the need for various plant food sources in vegetarian diets to meet protein requirements.
  2. Define protein-energy malnutrition (PEM).
  3. Discuss the conditions of Kwashiorkor and Marasmus with respect to protein consumption.
  4. Discuss the significance of albumin in nutritional assessment.