Albumin and Plasma Proteins

Plasma Proteins Overview - The Blood's Workhorses

Total plasma protein: 6.0-8.3 g/dL. Primarily synthesized in the liver (except γ-globulins from plasma cells).

• Core Functions:

  • Oncotic pressure (key: albumin)
  • Transport (e.g., hormones, drugs, lipids)
  • Buffering (acid-base balance)
  • Immunity (γ-globulins/antibodies)
  • Coagulation (e.g., fibrinogen)

• Major Classes & Primary Roles:

  • Albumin: Highest concentration; maintains oncotic pressure, transport.
  • Globulins:
    • α1, α2: Transport, protease inhibitors.
    • β: Transport (e.g., iron via transferrin, lipids via LDL).
    • γ (Immunoglobulins): Antibodies for immunity.
  • Fibrinogen: Essential for blood clotting.

• Analysis - SPEP: Serum Protein Electrophoresis separates into 5 bands: Albumin, α1, α2, β, and γ globulins.

⭐ Most plasma proteins are glycoproteins, except for albumin.

Albumin Focus - Osmotic & Transport Titan

• Most abundant plasma protein (~60% of total; 3.5-5.0 g/dL).
• Structure: Single polypeptide chain; no carbohydrate (CHO).
• Functions:
  • Major contributor to plasma oncotic pressure (~80%).
  • Versatile transport: Bilirubin, fatty acids, Ca²⁺, hormones, drugs (e.g., warfarin, salicylates).
  • Buffering (minor physiological role).
• Synthesis: Exclusively in the liver.
• Acute Phase Reactant: Negative (levels ↓ during inflammation).
• Hypoalbuminemia (<3.5 g/dL):
  • Causes: 📌 NALS (Nephrotic syndrome, Anorexia/Malnutrition, Liver cirrhosis, Severe burns/Skin loss).
  • Consequences: Generalized edema (peripheral, pulmonary, ascites).

  ⭐ Edema typically occurs when serum albumin levels fall below 2.0-2.5 g/dL.

• Hyperalbuminemia (>5.0 g/dL):
  • Causes: Primarily severe dehydration.
• Analbuminemia: Rare congenital disorder (virtual absence of albumin).

Globulins Deep Dive - Defense & Delivery Crew

• Heterogeneous group; separated by electrophoresis (e.g., SPEP).

⭐ A decreased or absent α1-globulin band on SPEP is highly suggestive of α1-antitrypsin deficiency.

Fibrinogen & Others - Clotting & Crisis Responders

• Fibrinogen (Factor I): Synthesized in the liver. Crucial for blood coagulation; converted to fibrin by thrombin.

  • Normal range: 200-400 mg/dL.
  • Conditions: Afibrinogenemia (absence), dysfibrinogenemia (abnormal function).

• Acute Phase Reactants (APRs): Proteins whose plasma levels change significantly with inflammation/tissue injury (stimuli: IL-1, IL-6, TNF-α).

  • Positive APRs (↑): C-Reactive Protein (CRP), Fibrinogen, Haptoglobin, Ceruloplasmin, Alpha-1 Antitrypsin (A1AT), Ferritin, Serum Amyloid A (SAA).
  • Negative APRs (↓): Albumin, Transferrin, Prealbumin (Transthyretin).

• Plasma Protein Electrophoresis (SPEP) Patterns:

  • Nephrotic Syndrome: ↓ Albumin, ↑ α2-macroglobulin, ↓ γ-globulins.
  • Liver Cirrhosis: Polyclonal gammopathy (broad ↑ γ-globulins), β-γ bridging.
  • Multiple Myeloma: Monoclonal gammopathy (M-spike).

⭐ In multiple myeloma, the M-spike is most commonly due to monoclonal IgG, followed by IgA.

High‑Yield Points - ⚡ Biggest Takeaways

• Albumin: Most abundant plasma protein, synthesized in the liver; maintains oncotic pressure and acts as a transporter.
• Hypoalbuminemia: Key cause of generalized edema.
• α1-Antitrypsin deficiency: Associated with early-onset emphysema and liver cirrhosis.
• Ceruloplasmin: Primary copper-carrying protein; decreased in Wilson's disease.
• Haptoglobin: Binds free hemoglobin; levels decrease significantly in intravascular hemolysis.
• Transferrin: Major iron transport protein; levels increase in iron-deficiency anemia.
• Acute phase reactants (e.g., CRP, fibrinogen) are altered during inflammation; albumin is a negative acute phase reactant (levels ↓).