Medical Laboratory Technology

🌟 (Gell and Coombs Classification)

Type→ Name →Immune Component→Mechanism of Damage →Onset →Examples

I→ Immediate (Anaphylactic) IgE + Mast cells/Basophils Allergen cross-links IgE on mast cells → Histamine release Seconds to minutes Asthma, Anaphylaxis, Hay fever, Urticaria, Food allergy

II → Cytotoxic (Antibody-mediated) IgG/IgM + Complement or ADCC Antibodies bind to antigens on cells → Cell destruction Minutes to hours Hemolytic anemia, Goodpasture's, Rheumatic fever, GBS

III→ Immune Complex IgG/IgM + Antigen + Complement Immune complexes deposit in tissues → Inflammation Hours to days SLE, Post-streptococcal GN, Serum sickness, Arthus reaction

IV→ Delayed-type (Cell-mediated) T cells (CD4+/CD8+) Sensitized T cells release cytokines → Macrophage activation or cytotoxicity 48–72 hours Tuberculosis, Contact dermatitis, Type 1 diabetes, MS

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🔍 Detailed Explanation of Each Type

✅ Type I – Immediate Hypersensitivity

Main antibody: IgE
Cells involved: Mast cells, basophils
Pathway: First exposure sensitizes → IgE binds to mast cells → Second exposure causes degranulation → Histamine release
Clinical signs: Swelling, itching, bronchospasm, hypotension (in anaphylaxis)

✅ Type II – Cytotoxic Hypersensitivity

Main antibodies: IgG, IgM
Pathway: Antibodies bind to cell surface antigens → Activate complement or ADCC → Cell lysis or opsonization
Key feature: Destruction of specific cells

Examples:
Autoimmune hemolytic anemia
Myasthenia gravis
Graves' disease (also has stimulatory antibodies)

✅ Type III – Immune Complex-Mediated Hypersensitivity

Main components: Antigen–antibody (IgG/IgM) complexes + complement
Pathway: Complexes deposit in small vessels → Complement activation → Neutrophil recruitment → Inflammation & tissue damage

Examples:
Systemic lupus erythematosus (SLE)
Post-streptococcal glomerulonephritis
Serum sickness
Arthus reaction (localized)

✅ Type IV – Delayed-type Hypersensitivity

Main cells: T lymphocytes (CD4+ helper T cells, CD8+ cytotoxic T cells)
Pathway: Antigen-presenting cells activate T cells → Cytokine release or direct killing → Tissue damage
Not antibody mediated

Examples:
Tuberculin skin test (Mantoux test)
Contact dermatitis (e.g., poison ivy, nickel)
Type 1 diabetes mellitus
Multiple sclerosis

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📌 Mnemonic to Remember Types:

"ACID"

A – Type I: Anaphylactic (IgE)

C – Type II: Cytotoxic (IgG/IgM)

I – Type III: Immune complex

D – Type IV: Delayed (T-cell)

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(IgG) is the most abundant type of antibody in the human body and plays a crucial role in the immune system. Here are detailed insights:

Basic Overview:

Full Name: Immunoglobulin G
Type: Monomeric antibody (Y-shaped)
Molecular Weight: ~150 kDa
Serum Concentration: 7–16 g/L (most abundant immunoglobulin in circulation, ~75–80% of serum antibodies)

Structure:
Composed of:
2 heavy chains (γ chains)
2 light chains (κ or λ)

Contains:
Fab regions (antigen-binding)
Fc region (binds to Fc receptors on immune cells and complement proteins)

Subclasses of IgG:
There are four subclasses, differing in structure and function:
1. IgG1 – 60–70% of total IgG; responds to protein antigens (e.g., viruses, toxins)
2. IgG2 – 20–25%; targets polysaccharide antigens (e.g., bacterial capsules)
3. IgG3 – 5–10%; effective in complement activation
4. IgG4 – ~4%; involved in chronic antigen exposure, least inflammatory

Functions:
Neutralization: Binds and neutralizes toxins, viruses, and bacteria
Opsonization: Marks pathogens for destruction by phagocytes
Complement Activation: IgG1, IgG3 initiate classical complement pathway
Antibody-Dependent Cellular Cytotoxicity (ADCC): Activates NK cells via Fc receptors
Immune Memory: Produced during secondary immune response
Placental Transfer: Only Ig class that crosses the placenta to provide passive immunity to the fetus

Clinical Significance:

Elevated IgG:
Chronic infections (e.g., tuberculosis)
Autoimmune diseases (e.g., lupus, rheumatoid arthritis)
Multiple myeloma
Chronic liver disease

Decreased IgG:
Immunodeficiencies (e.g., Common Variable Immunodeficiency – CVID)
Protein-losing conditions (e.g., nephrotic syndrome)
Certain leukemias

IgG Testing:
Quantitative IgG test: Measures serum IgG levels
IgG subclass test: Analyzes each subclass separately
Specific IgG antibodies: Used to detect past exposure or immunity to specific pathogens (e.g., Hepatitis B, COVID-19)

Therapeutic Uses:
IVIG (Intravenous Immunoglobulin):
Prepared from pooled donor plasma
Used to treat autoimmune disorders, immunodeficiencies, and inflammatory diseases

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, including types, causes, symptoms, and lab diagnosis:

What is Anemia?
Anemia is a condition characterized by a decrease in the total amount of red blood cells (RBCs) or hemoglobin (Hb) in the blood, leading to reduced oxygen-carrying capacity.

Classification of Anemia

1. Based on RBC Size (MCV - Mean Corpuscular Volume):

Microcytic anemia (MCV < 80 fL)
Iron Deficiency anemia
Thalassemia
Anemia of chronic disease (occasionally)
Sideroblastic anemia

Normocytic anemia (MCV 80–100 fL)
Acute blood loss
Hemolytic anemia
Anemia of chronic disease
Aplastic anemia

Macrocytic anemia (MCV > 100 fL)
Vitamin B12 deficiency
Folate deficiency
Alcoholism
Liver disease
Hypothyroidism
Myelodysplastic syndrome

Etiological Classification:
Blood loss: Acute (trauma), Chronic (GI bleeding, menorrhagia)

Decreased RBC production:
Nutritional deficiencies (Iron, B12, folate)
Bone marrow failure
Chronic diseases

Increased RBC destruction:
Hemolytic anemia (hereditary: spherocytosis, G6PD; acquired: autoimmune)

Common Symptoms:
Fatigue, weakness
Pallor (skin, conjunctiva)
Dyspnea
Palpitations
Dizziness
Pica (in iron deficiency)
Neurological symptoms (in B12 deficiency)

Lab Diagnosis of Anemia

1. Complete Blood Count (CBC)

Hemoglobin (Hb): Low in anemia

Hematocrit (Hct): Usually reduced

RBC Count: Decreased

MCV: Helps classify anemia (micro, normo, macrocytic)

MCH/MCHC: Assess hemoglobin content per RBC

RDW: Red cell distribution width – increased in mixed or iron-deficiency anemia

2. Peripheral Blood Smear

Morphology of RBCs:

Microcytic, hypochromic (iron deficiency)

Macrocytic (megaloblastic)

Spherocytes, schistocytes (hemolysis)

Target cells (thalassemia)

Hypersegmented neutrophils (B12/folate deficiency)

3. Reticulocyte Count

Indicates bone marrow response:

Low in production defects

High in hemolysis or blood loss

4. Iron Studies

Serum iron: Low in iron deficiency

TIBC (Total iron-binding capacity): Increased in iron deficiency

Ferritin: Low in iron deficiency; high in anemia of chronic disease

Transferrin saturation: Low in iron deficiency

5. Vitamin B12 & Folate Levels

Low in megaloblastic anemia

6. Hemolysis Workup

LDH: Increased

Indirect bilirubin: Increased

Haptoglobin: Decreased

Coombs test: Positive in autoimmune hemolytic anemia

7. Bone Marrow Examination

If diagnosis unclear or for aplastic anemia, leukemia, etc.

Erythroid hyperplasia in hemolysis or megaloblastic anemia

8. Special Tests

Hb electrophoresis: Thalassemia, sickle cell anemia

G6PD assay: G6PD deficiency

Osmotic fragility test: Hereditary spherocytosis

Treatment Overview

Iron deficiency: Oral or IV iron

B12/Folate deficiency: Supplements

Hemolytic anemia: Treat underlying cause, steroids, transfusions

Chronic disease anemia: Manage underlying disease

Severe anemia: Blood transfusion if Hb critically low

G6PD stands for Glucose-6-Phosphate Dehydrogenase, an enzyme found in red blood cells. It plays a crucial role in protecting red blood cells from damage and premature destruction.

Key Points about G6PD:

1. Function:

G6PD is essential for the pentose phosphate pathway, which helps produce NADPH, a molecule that protects red blood cells from oxidative stress.

2. G6PD Deficiency:

A genetic condition where the body doesn't produce enough of the enzyme.

Most common in males (X-linked inheritance).

Can lead to hemolytic anemia (destruction of red blood cells), especially when exposed to certain triggers.

3. Common Triggers:

Certain medications (e.g., sulfa drugs, antimalarials)

Infections

Fava beans (leading to “favism”)

4. Symptoms of G6PD Deficiency:

Jaundice

Dark urine

Fatigue

Rapid heart rate

Shortness of breath

5. Diagnosis:

Blood tests to measure G6PD enzyme activity.

Often included in newborn screening in some countries.

6. Management:

Avoidance of known triggers.

Supportive care during hemolytic episodes (hydration, oxygen, sometimes blood transfusion).