Clinical Chem pt 3

Plasma Proteins Overview

Plasma proteins are primarily synthesized in the liver.
The immune system is capable of producing other plasma proteins as well.
There are over 200 different types of plasma proteins identified.
The major plasma proteins of importance include:
- Albumin
- Globulin
- Fibrinogen

Functions are numerous; however, specific details about each function may not be prioritized in the VTNE.
Due to the vast number of plasma proteins, only key ones are emphasized in veterinary contexts.

Albumin is the smallest and most significant plasma protein, constituting 35% to 50% of total plasma proteins.
In cases of hypoproteinemia, the primary cause is often loss of albumin.
Loss can occur through:
- Protein-Losing Enteropathy (PLE)
- Protein-Losing Nephropathy (PLN)
Albumin functions as the major binding protein in blood, maintaining osmotic pressure of plasma spaces.
- Loss of albumin can severely disrupt the body's metabolic homeostasis.

Globulins have various functions, categorized into different groups:
- Alpha globulins are typically involved in transport functions.
- Beta globulins transport iron and participate in fibrin formation.
Immunoglobulins within this group are crucial for immune responses, specifically for antibody production.
Key immunoglobulins to know include:
- IgG, IgE, IgA
- IgM serves a role related to antibodies from mother to offspring.

Fibrinogen is produced by liver cells and acts as a precursor to fibrin, crucial for clot formation.
Low fibrinogen levels can lead to unstable clot development.
Preferred testing method for fibrinogen is using EDTA plasma to avoid depletion in serum separator tubes or red top tubes.

Total protein levels can be measured using a refractometer, which reads:
- Fibrinogen
- Albumin
- Globulin
Units for measuring total protein are in grams per deciliter (g/dL), while urine specific gravity lacks units.
- Refractometer scales: One scale measures total protein, another measures urine specific gravity (0 to 1.050).

Dehydration: Increases total protein levels, particularly globulins, which are often the first to rise.
Overhydration: Can give falsely low protein readings by diluting the plasma proteins.
Hemic Hemolysis: Profound hemolysis may cause elevated protein readings due to lipid interference.

Total protein levels are significant when evaluating:
- Dehydration
- Edema (fluid accumulation)
- Diarrhea (loss of protein)
Changes in albumin levels usually indicate dehydration or liver dysfunction, while globulin levels can indicate immune response or hydration status.
Correct interpretation is critical in various conditions such as liver disease, renal disease, and protein-losing disorders.

PLN leads to losses of primarily albumin due to a compromise in kidney filtration.
- GFR (glomerular filtration rate) assesses kidney function; damage causes larger gaps in filtration which allows albumin to leak into the urine.
- Typically, glucose and larger globulin proteins remain retained until significant permeability occurs.

PLE involves losses of both albumin and globulins due to increased intestinal permeability.
Common causes of PLE include various intestinal diseases or conditions disrupting the intestinal wall integrity.

Diagnosis of protein-losing disorders often requires:
- CBC (Complete Blood Count) to check for anemia or low lymphocytes.
- Fecal exam to identify potential underlying infections or conditions.
A typical confirmatory examination might involve multiple fecal tests to ascertain the cause of protein loss.

Remember the primary effects of hydration on total protein levels and the differentiation between PLE and PLN regarding protein loss.
The liver’s role in producing plasma proteins is pivotal; dysfunction can lead to widespread metabolic issues.
Proper methods of measurement and interpretation of plasma protein levels are essential for diagnosing and managing conditions in veterinary practice.