HYPERSENSITIVITY – SKIN TEST & SEROLOGICAL TESTS

B.Sc Nursing Microbiology Notes (INC Syllabus) – Exam Oriented, Mobile Friendly

1. INTRODUCTION

Hypersensitivity is an exaggerated immune response of the body against an antigen (allergen) that results in tissue damage or clinical symptoms.

Normally, the immune system protects the body, but sometimes the immune response becomes overactive, causing conditions such as:

• Allergy

• Asthma

• Drug reactions

• Autoimmune disorders

Importance in Nursing Practice

Understanding hypersensitivity helps nurses to:

• Identify allergic reactions early

• Prevent anaphylaxis

• Perform skin tests safely

• Interpret serological test results

• Monitor patients receiving vaccines, antibiotics, or blood transfusion

Role in Disease Prevention

• Identification of allergens helps avoid exposure

• Early diagnosis prevents severe complications

• Screening tests help detect immune disorders

2. DEFINITION

Hypersensitivity Definition (Exam Ready)

Hypersensitivity is an exaggerated or abnormal immune response to an antigen that causes tissue damage or disease.

Skin Test Definition

Skin test is a diagnostic method used to detect hypersensitivity reaction by introducing antigen into the skin.

Serological Test Definition

Serological test is a laboratory test used to detect antigen or antibody in blood serum.

3. CLASSIFICATION OF HYPERSENSITIVITY

Hypersensitivity reactions are classified into 4 types:

Type	Name	Mechanism	Example
Type I	Immediate	IgE mediated	Anaphylaxis
Type II	Cytotoxic	IgG/IgM destroy cells	Hemolytic anemia
Type III	Immune complex	Antigen-antibody complex deposition	Rheumatoid arthritis
Type IV	Delayed	T-cell mediated	Contact dermatitis

4. CHARACTERISTICS OF HYPERSENSITIVITY

Common features:

• Occurs after antigen exposure

• Involves immune system

• Causes tissue damage

• May be mild or severe

• May be immediate or delayed

Important Immune Components

Component	Role
Antigen	triggers immune response
Antibody	reacts with antigen
Mast cells	release histamine
Histamine	causes inflammation
T lymphocytes	delayed response

5. GROWTH / DEVELOPMENT PROCESS (IMMUNE RESPONSE DEVELOPMENT)

Hypersensitivity develops in two stages:

Sensitization stage

First exposure → immune system recognizes antigen → antibody formation

Reaction stage

Second exposure → antigen reacts with antibody → symptoms appear

6. PATHOGENESIS / MECHANISM

Mechanism of Hypersensitivity

Allergen entry → immune activation → antibody production → antigen-antibody reaction → release of chemicals (histamine) → symptoms

Type I Hypersensitivity Mechanism

Allergen → IgE production → mast cell activation → histamine release → inflammation

Examples:

• dust allergy

• food allergy

7. MODES OF EXPOSURE (TRANSMISSION)

Allergens enter body through:

Mode	Example
Inhalation	pollen, dust
Ingestion	food allergy
Injection	drugs, vaccines
Skin contact	latex
Blood transfusion	transfusion reaction

8. CLINICAL MANIFESTATIONS

Common symptoms:

Mild reactions

• itching

• rash

• sneezing

• redness

• swelling

Severe reactions

• bronchospasm

• hypotension

• anaphylactic shock

• difficulty breathing

9. DIAGNOSTIC METHODS

Hypersensitivity diagnosed by:

• Skin tests

• Serological tests

• History taking

• Physical examination

9A. SKIN TEST

Skin test is used to identify allergic reaction.

Types of Skin Test

Test	Purpose
Prick test	detect allergy
Intradermal test	detect drug sensitivity
Patch test	detect contact allergy
Tuberculin test	detect TB exposure

Procedure of Skin Test

Antigen injected into skin → observe reaction → redness/swelling indicates positive test

Example

Mantoux test for tuberculosis

Advantages

• Simple

• Rapid result

• inexpensive

9B. SEROLOGICAL TESTS

Serological tests detect antibodies in blood.

Common Serological Tests

Test	Purpose
ELISA	detect antigen or antibody
Agglutination test	antigen-antibody reaction
Precipitation test	antigen detection
Complement fixation	antibody detection
Neutralization test	virus detection

Principle

Antigen + antibody reaction → visible reaction → positive result

10. PREVENTION AND CONTROL

Prevent hypersensitivity by:

• avoiding allergen exposure

• careful drug administration

• vaccination safety

• allergy testing

• patient education

Hospital precautions:

• check drug history

• perform sensitivity test before antibiotic

• monitor vaccine reaction

11. NURSING RESPONSIBILITIES

Nurse plays important role in hypersensitivity management.

Before test

• collect patient history

• check allergy history

• explain procedure

During test

• maintain aseptic technique

• observe reaction

• ensure patient comfort

After test

• monitor complications

• document findings

• report abnormal reaction

Emergency management

manage anaphylaxis:

• oxygen

• adrenaline

• IV fluids

12. COMMON DISEASES RELATED TO HYPERSENSITIVITY

Disease	Type
Asthma	Type I
Allergy	Type I
Anaphylaxis	Type I
Hemolytic anemia	Type II
Rheumatoid arthritis	Type III
Contact dermatitis	Type IV

13. EXAM KEY POINTS

1. Hypersensitivity is exaggerated immune response

2. Four types – Type I, II, III, IV

3. Skin test detects allergy

4. Mantoux test used for TB detection

5. ELISA detects antibodies

6. Histamine causes inflammation

7. Nurse monitors allergic reaction

8. Anaphylaxis is medical emergency

14. SUGGESTED DIAGRAM / FLOWCHART

Students should practice drawing:

1. Types of hypersensitivity chart

2. Antigen antibody reaction diagram

3. Skin test procedure diagram

4. Mechanism of Type I hypersensitivity

15. QUICK REVISION TABLE

Test	Detects	Example
Skin test	allergy	TB test
ELISA	antibody	HIV
Agglutination	antigen	typhoid
Patch test	contact allergy	dermatitis