L7 - Plasma Proteins

What are the Main Components of Plasma?

Plasma contains:

1. Water

2. Biochemical constituents, including proteins, electrolytes, enzymes, and metabolites.

What is the Difference between Plasma and Serum?

Plasma:

• Obtained from anticoagulated blood(e.g., EDTA purple-top tube)

• Contains all proteins, including fibrinogen and clotting factors

  • Plasma total protein is typically slightly higher than serum total protein

Serum:

• Obtained blood after blood clots (e.g., red-top tube)

• Lacks fibrinogen and clotting factors consumed during clot formation

Use the same sample type when monitoring protein trends

What are the Main Plasma Protein Groups, their Sites of Synthesis, and their Functions?

1. Albumin:

   • Synthesized by hepatocytes

   • Maintains oncotic pressure and transports substances such as bilirubin

2. Gamma globulins (immunoglobulins):

   • Synthesized by plasma cells

   • Function as antibodies in adaptive immunity

3. Alpha and beta globulins:

   • Primarily synthesized by hepatocytes

   • Include acute phase, transport, complement, clotting, and lipoproteins

Why is Albumin Important for Maintaining Oncotic Pressure?

Albumin is the most abundant individual plasma protein and helps retain water within blood vessels

• Severe hypoalbuminemia can decrease oncotic pressure, resulting in edema or body cavity effusions

How are Plasma Proteins Measured Using Refractometry?

Refractometry measures the refractive index of plasma, which correlates with dissolved solute concentration, primarily proteins

• It is used to estimate total plasma protein (TPP), with fibrinogen measurable after heat precipitation

What Factors can Interfere with Refractometric Protein Measurements?

These substances affect light refraction independently of protein concentration.

• High glucose, sodium, or urea concentrations can falsely increase TPP

• Hemolysis and lipemia can interfere with readings

How are Serum Total Protein, Albumin, and Globulins Measured?

• Total protein: Biuret method

• Albumin: Bromocresol green method

  • May vary by species, particularly birds, and can be affected by bilirubin or certain drugs

• Globulins: Calculated as (total protein − albumin)

• Albumin: Globulin (A/G) ratio: Used to identify disproportionate protein changes

What is Serum Protein Electrophoresis (SPE), and What Does It Measure?

SPE separates serum proteins into albumin, alpha-1, alpha-2, beta, and gamma fractions based on their electrophoretic properties

• SPE helps identify which protein fractions are increased or decreased

1. Albumin: Largest peak in healthy animals

2. Alpha and beta fractions: Primarily acute phase and other non-immunoglobulin proteins

3. Gamma fraction: Primarily immunoglobulins

*What Terminology Describes Increased and Decreased Protein Concentrations?

Hyperproteinemia / Hypoproteinemia:

• Increased / decreased total protein

Panhyperproteinemia / Panhypoproteinemia:

• Both albumin and globulins increased / decreased

Hyperalbuminemia / Hypoalbuminemia:

• Increased / decreased albumin

Hyperglobulinemia / Hypoglobulinemia:

• Increased / decreased globulins

Hyperfibrinogenemia / Hypofibrinogenemia:

• Increased / decreased fibrinogen

Hypergammaglobulinemia / Hypogammaglobulinemia:

• Increased / decreased gamma globulins

What is the Difference between Relative and True (Absolute) Protein Changes?

Relative changes:

• Protein mass remains unchanged, BUT plasma water volume changes

  • Dehydration → Apparent increased protein concentration

  • Overhydration → Apparent decreased protein concentration

True changes:

• Actual protein mass changes due to:

  • Altered synthesis

  • Increased loss

  • Changes in intake/utilization

How does Age Affect Total Protein Concentrations?

Neonates have lower total protein concentrations than adults

• Colostrum ingestion causes a temporary increase in immunoglobulins, especially IgG

• Maternal immunoglobulins gradually decline as endogenous protein and antibody synthesis increases

• Failure of passive transfer prevents the expected post-colostrum increase in proteins

• Age-specific reference intervals are important when interpreting protein values.

What is the Primary Mechanism of Hyperalbuminemia?

Dehydration (relative increase) is the only clinically relevant cause of hyperalbuminemia

• The liver does not normally overproduce albumin

What Laboratory Pattern Suggests Dehydration?

CBC

• Hematocrit (HCT) may also increase

• Increase plasma proteins

CHEM

• Increased total protein

• Increased albumin

• Normal or proportionately increased globulins

Clinical findings

• Tacky mucous membranes, decreased skin turgor, and sunken eyes support dehydration

What are the Major Mechanisms of Hyperglobulinemia?

Relative increase: Dehydration

True increase:

• Increased gamma globulin production due to chronic inflammation or lymphoid neoplasia

• Increased alpha and beta globulin production during an acute phase response

What is the Difference between Polyclonal and Monoclonal Gammopathy?

Polyclonal gammopathy:

• Broad-based gamma peak on SPE caused by increased production of multiple immunoglobulins

• Commonly due to chronic inflammation

Monoclonal gammopathy:

• Narrow-based gamma peak on SPE caused by a abnormal immunoglobulin population

• Commonly associated with lymphoid neoplasia

What are the Major Causes of Polyclonal and Monoclonal Gammopathies?

Polyclonal:

• Chronic inflammation and persistent antigenic stimulation, including infectious diseases such as feline infectious peritonitis (FIP)

Monoclonal:

• Lymphoid neoplasia, particularly plasma cell myeloma

• Non-neoplastic monoclonal gammopathies may also occur with infections, especially canine ehrlichiosis and leishmaniasis

Why can Hyperglobulinemia be accompanied by Hypoalbuminemia?

During inflammation, albumin synthesis may decrease because albumin is a negative acute phase protein

• The lecture also describes a compensatory reduction in albumin synthesis during marked hyperglobulinemia to help balance oncotic pressure.

*What Protein Patterns Help Distinguish Dehydration from Inflammation or Neoplasia?

Interpret these patterns alongside clinical findings and hematocrit:

• Increased albumin with normal or increased globulins

→ Dehydration

• Increased globulins with normal or decreased albumin

→ Chronic inflammation, lymphoid neoplasia, or certain infections

What is the Acute Phase Response, and How Does It Affect Plasma Proteins?

Inflammation stimulates cytokine-mediated changes in hepatic protein synthesis

• Positive acute phase proteins increase

• Negative acute phase proteins decrease

• Alpha and beta globulin fractions may increase on SPE

Most acute phase proteins are present in relatively low concentrations, so their increases may have little effect on total protein

What are the Major Positive and Negative Acute Phase Proteins?

Positive (increase):

• Fibrinogen

• C-reactive protein

• Serum amyloid A

• Haptoglobin

• Alpha-1-acid glycoprotein

• Ceruloplasmin

• Alpha-2-macroglobulin

Negative (decrease):

• Albumin

• Transferrin

PRACTICE QUESTION: A 9-month-old filly has a cough and nasal discharge

ANSWER → Hyperproteinemia due to hyperglobulinemia

• Likely chronic inflammation due to upper airway infection

Why is Fibrinogen Clinically Important in Large Animals?

Fibrinogen is the most abundant acute phase protein and increases during acute or chronic inflammation

• Its concentration can significantly increase total plasma protein, making it a useful inflammatory marker in large animals

What is the Protein:Fibrinogen Ratio, and How is It Interpreted?

Protein:Fibrinogen Ratio = Total plasma protein (g/dL) / Fibrinogen (g/dL)

• Ratio ≥ 15: Proportionate increase, suggesting dehydration

• Ratio < 15: Disproportionate fibrinogen increase, suggesting inflammation

Fibrinogen must be converted from mg/dL to g/dL before calculation

PRACTICE QUESTION: A 9-month-old filly has a cough and nasal discharge

ANSWER → Hyperproteinemia due to hyperglobulinemia, most likely from chronic inflammation associated with an upper respiratory infection

• Plasma protein: 10.4 g/dL

• Fibrinogen: 900 mg/dL; Convert fibrinogen: 900 mg/dL = 0.9 g/dL

• 10.4/0.9 = 11.5

  • The ratio is below 15, indicating a disproportionate increase in fibrinogen

• Albumin and HCT are within reference intervals, making dehydration less likely as the primary explanation

PRACTICE QUESTION: A 2 year old quarter horse with colic is moderately dehydrated on examination

ANSWER → Dehydration

• HCT: 48% (30–46)

• Plasma protein: 9.2 g/dL (5.8–8.7)

• Fibrinogen: 600 mg/dL (100–400); Convert fibrinogen: 600 mg/dL = 0.6 g/dL

• 9.2/0.6 = 15.3

  • The ratio is ≥ 15, indicating a proportionate increase in plasma protein relative to fibrinogen, consistent with the clinical findings

What are the Major Mechanisms of Hypoalbuminemia?

Decreased synthesis:

• Hepatic insufficiency

• Acute phase response

• Compensatory response to marked hyperglobulinemia

Increased loss:

• Renal loss through glomerular disease

• Gastrointestinal loss (protein-losing enteropathy, diarrhea, malabsorption)

• Blood loss, exudates, or vasculitis

Decreased intake or increased utilization:

• Malnutrition or cachexia

What are the Major Mechanisms of Hypoglobulinemia?

Decreased synthesis:

• Immunodeficiencies causing hypogammaglobulinemia

• Hepatic insufficiency (decreased alpha and beta globulins)

Increased loss:

• Gastrointestinal (protein-losing enteropathy, diarrhea, malabsorption)

• Blood loss, Hemorrhage or exudates

Decreased intake:

• Failure of passive transfer in neonates

What are the Major Patterns of Hypoproteinemia and their Possible Causes?

Panhypoproteinemia (decreased albumin and globulins):

• Hemorrhage, gastrointestinal protein loss, or dilution

Hypoalbuminemia with normal or increased globulins:

• Renal protein loss, decreased albumin synthesis, or inflammation

Hypoglobulinemia with normal or increased albumin:

• Immunodeficiency or failure of passive transfer

PRACTICE QUESTION: A 6-year-old Siberian Husky was hit by a car yesterday and today collapsed

ANSWER → Hemorrhagic blood loss

• Decreased HCT indicates anemia

• Decreased albumin and globulins indicate panhypoproteinemia

• Together with the history of trauma, these findings strongly suggest hemorrhage

Case 1 — A Dog with Vomiting

A 5-year-old dog presents with vomiting, tacky mucous membranes, and decreased skin turgor.

QUESTION: What is the most likely cause of the increased total protein?

ANSWER → Dehydration (relative hyperproteinemia)

• Albumin and globulins are both increased

• HCT and physical examination support reduced plasma water volume

Case 2 — A Cat with Chronic Inflammation

A cat has persistent fever and weight loss.

QUESTION: Which protein group explains the hyperproteinemia, and what mechanism is most likely?

ANSWER → Hyperglobulinemia due to increased immunoglobulin production, consistent with chronic inflammation

• Albumin is mildly decreased, which can occur because albumin is a negative acute phase protein

Case 3 — A Dog with Protein Loss

A dog has marked proteinuria, with no evidence of dehydration.

QUESTION: What is the most likely mechanism of hypoalbuminemia?

ANSWER → Renal protein loss through the glomeruli

• Albumin is markedly decreased while globulins remain within reference limits, supporting selective albumin loss

Case 4 — A Dog with Chronic Diarrhea

A dog has chronic diarrhea and weight loss.

QUESTION: What is the most likely cause of the hypoproteinemia?

ANSWER → Protein-losing enteropathy

• Both albumin and globulins are decreased (panhypoproteinemia), consistent with gastrointestinal protein loss

Case 5 — A Horse with Fever

An adult horse has fever, nasal discharge, and inflammatory changes on its CBC.

QUESTION: Calculate the protein:fibrinogen ratio. Does it support inflammation or dehydration?

ANSWER → Since the ratio is below 15, it supports inflammation

• 1000 mg/dL = 1.0 g/dL

• Ratio = 9.0 / 1.0 = 9.0

Case 6 — A Dehydrated Horse

A horse has colic, decreased skin turgor, and dry mucous membranes.

QUESTION: Calculate the protein:fibrinogen ratio and identify the likely mechanism.

ANSWER → The ratio is at least 15, and the increased HCT and dehydration signs support a relative increase due to dehydration

• 400 mg/dL = 0.4 g/dL

• Ratio = 9.6 / 0.4 = 24

Case 7 — A Dog with a Plasma Cell Tumor

A dog has marked hyperglobulinemia. Serum protein electrophoresis shows a tall, narrow gamma peak.

QUESTION: What type of gammopathy is present, and which disease category is strongly suspected?

ANSWER → Monoclonal gammopathy, raising concern for lymphoid neoplasia such as plasma cell myeloma

• Certain infections can also produce a monoclonal pattern, so the finding alone is not diagnostic

Case 8 — A Dog After Fluid Therapy

A hospitalized dog receives excessive IV fluids. There is no evidence of hemorrhage or gastrointestinal protein loss.

QUESTION: What is the most likely reason for the low total protein and HCT?

ANSWER → Overhydration causing hemodilution

• The plasma water volume increases, making protein and red cell concentrations appear lower without necessarily reducing their total mass

Case 9 — A Dog with Acute Blood Loss

A dog presents after trauma with weakness and evidence of internal bleeding.

QUESTION: What is the most likely explanation for the combined abnormalities?

ANSWER → Hemorrhagic blood loss

• Decreased HCT plus decreased albumin and globulins indicates loss of red cells and plasma proteins

• The timing and fluid shifts affect when these changes become measurable.

Case 10 — A Neonatal Foal

A newborn foal did not nurse adequately after birth. Its serum total protein and immunoglobulin concentrations remain low.

QUESTION: What mechanism best explains these findings, and why is age important?

ANSWER → Failure of passive transfer due to inadequate colostrum intake

• Neonates normally acquire maternal IgG through colostrum, causing an early increase in immunoglobulin concentration

• Age-specific reference intervals are necessary

Table 1. Major Plasma Proteins — Synthesis & Function

Protein	Site of Synthesis	Main Function
Albumin	Hepatocytes	Maintains oncotic pressure; transports bilirubin and other substances
Gamma globulins (Ig)	Plasma cells	Antibodies; adaptive immunity
Alpha & beta globulins	Primarily hepatocytes	Acute phase response, transport, complement, clotting
Fibrinogen	Hepatocytes	Coagulation; positive acute phase protein

Table 2. Plasma vs. Serum & Laboratory Methods

Feature	Plasma	Serum
Collection	Anticoagulated blood (EDTA)	Clotted blood (no anticoagulant)
Tube	Purple-top	Red-top
Fibrinogen / clotting factors	Present	Consumed during clotting
Total protein measurement	Refractometry	Biuret method
Albumin measurement	Not routinely measured by refractometry	Bromocresol green
Additional measurements	Fibrinogen, protein:fibrinogen ratio	Calculated globulins, A/G ratio

Important: Plasma total protein is usually slightly higher than serum total protein because plasma contains fibrinogen and clotting factors

• Avoid switching between plasma and serum measurements when monitoring trends

Table 3. Causes of Increased vs. Decreased Plasma Proteins

Protein	Increased (Hyper-)	Decreased (Hypo-)
Total protein	Dehydration, increased globulin production	Overhydration, hemorrhage, protein loss
Albumin	Dehydration (relative)	Decreased synthesis, renal/GI loss, hemorrhage, inflammation
Globulins	Dehydration, chronic inflammation, lymphoid neoplasia	Immunodeficiency, protein loss, failure of passive transfer
Gamma globulins	Chronic antigenic stimulation, lymphoid neoplasia	Immunodeficiency, failure of passive transfer
Fibrinogen	Acute/chronic inflammation, dehydration (relative)	Consumption or impaired production

Key distinction:

• Relative changes = Change in plasma water volume.

• Absolute changes = Change in actual protein mass.

Table 3A. Causes of Increased Protein Concentrations (Hyperproteinemia)

Protein	Mechanism	Causes
Total protein ↑	Relative increase	Dehydration
	True increase	Increased globulin production
Albumin ↑	Relative increase ONLY	Dehydration
Globulins ↑	Relative increase	Dehydration
	Increased production	Chronic inflammation, lymphoid neoplasia
Gamma globulins ↑	Increased antibody production	Chronic inflammation (polyclonal), lymphoid neoplasia (monoclonal)
Alpha & beta globulins ↑	Increased production	Acute phase response
Fibrinogen ↑	Increased production	Acute or chronic inflammation

Remember: Hyperalbuminemia is caused by dehydration, NOT increased albumin synthesis.

Table 3B. Causes of Decreased Protein Concentrations (Hypoproteinemia)

Protein	Mechanism	Causes
Total protein ↓	Relative decrease	Overhydration
	True decrease	Decreased albumin and/or globulin concentrations
Albumin ↓	Decreased synthesis	Hepatic insufficiency, acute phase response, compensatory response to hyperglobulinemia
	Increased loss	Hemorrhage, renal disease, gastrointestinal disease, exudates
	Decreased intake / increased utilization	Malnutrition, cachexia
Globulins ↓	Decreased synthesis	Immunodeficiency, hepatic insufficiency
	Increased loss	Hemorrhage, gastrointestinal disease, exudates
	Decreased intake	Failure of passive transfer in neonates

Table 4. Laboratory Protein Patterns & Clinical Interpretation

Laboratory Pattern	Most Likely Interpretation
↑ Albumin + ↑ Globulins + ↑ HCT	Dehydration
↑ Albumin + normal globulins	Dehydration
↑ Globulins + normal/↓ albumin	Chronic inflammation, infection, or lymphoid neoplasia
↑ Gamma globulins + broad SPE peak	Polyclonal gammopathy; commonly chronic inflammation
↑ Gamma globulins + narrow SPE peak	Monoclonal gammopathy; commonly lymphoid neoplasia, occasionally infection
↑ Fibrinogen + protein:fibrinogen ratio <15	Inflammation
↑ Total plasma protein + ratio ≥15	Proportionate increase; supports dehydration
↓ Albumin + ↓ Globulins + ↓ HCT	Hemorrhage
↓ Albumin + normal/↑ Globulins	Renal protein loss, decreased synthesis, or inflammation
↓ Albumin + ↓ Globulins	Hemorrhage, GI protein loss, or dilution

Exam tip: Always interpret protein values together with HCT, clinical signs, and the individual albumin and globulin concentrations. Total protein alone cannot identify the underlying mechanism.

Table 5. Acute Phase Proteins & Serum Protein Electrophoresis

Protein / Pattern	Change	Clinical Significance
Positive acute phase proteins	↑ Fibrinogen, CRP, SAA, haptoglobin, etc.	Acute or chronic inflammation
Negative acute phase proteins	↓Albumin, transferrin	Inflammatory response
Alpha / beta SPE fractions	↑	Increased acute phase protein production
Broad gamma peak	↑	Polyclonal gammopathy; commonly chronic inflammation
Narrow gamma peak	↑	Monoclonal gammopathy; commonly lymphoid neoplasia, but some infections

Protein:Fibrinogen Ratio — Quick Reference

Ratio	Interpretation
≥ 15	Proportionate increase; supports dehydration
<15	Disproportionate fibrinogen increase; supports inflammation

This ratio is particularly useful in large animals.

The ONLY Table I Want You to Memorize

Disease / Condition	Albumin	Globulins	WHY?
Dehydration	↑	↑	Less water
Chronic inflammation	↓ or normal	↑	More antibodies
Lymphoid neoplasia	↓ or normal	↑	Abnormal immunoglobulin production
Hemorrhage	↓	↓	Losing blood and proteins
Kidney disease	↓	Normal	Albumin lost in urine
GI disease	↓	↓	Proteins lost through intestines

1. Check total protein: Is it increased or decreased?

2. Check albumin and globulins: Which one is causing the change?

3. Check HCT and clinical signs: Does dehydration, dilution, or hemorrhage fit?

4. Identify the mechanism: Water change, increased/decreased production, or protein loss.

5. For large animals: If fibrinogen is provided, calculate the protein:fibrinogen ratio.