Tuberculosis cutaneous examination uses procedure and results

The Tuberculin Skin Test (PPD) is a simple and effective test used to detect whether the body has been exposed to the tuberculosis bacteria. It is considered one of the most important medical tools for early detection of infection, especially in individuals at higher risk. Whether you are experiencing symptoms or undergoing a routine screening, this test plays a crucial role in identifying the disease early.we will explore how the PPD test is performed, its importance, and how to interpret the results to be prepared for any necessary next steps in treatment.

What is the Tuberculin Skin Test (PPD)?
The Tuberculin Skin Test (PPD) is used to detect whether the body has been exposed to the tuberculosis bacteria (Mycobacterium tuberculosis). This test does not always detect active TB disease but shows if the body has encountered the bacteria in the past and developed immunity.

1. What is the PPD Test?
The PPD test, also known as the Mantoux test, is a simple procedure where a small amount of tuberculin protein is injected under the skin of your forearm. It helps determine if you have been exposed to tuberculosis or similar diseases.

2. How is the test performed?

A healthcare professional injects a small amount of PPD under the skin of the forearm.
After 48–72 hours, you return to the clinic to check the injection site for swelling or redness.

3. What do the results mean?

Very small swelling or no reaction usually indicates a negative result, meaning no infection.
Significant swelling or redness suggests a positive result, meaning exposure to TB bacteria.
Note: Results are not 100% definitive; chest X-rays or blood tests may be needed for confirmation.

4. Are there symptoms after the test?

Generally, there are no serious side effects.
Mild itching or tingling at the injection site may occur.
A small raised area (1–2 cm) is normal.

5. Can results be inaccurate?

False positive: Previous BCG vaccination or immune system disorders.
False negative: Weak immune system or testing too soon after TB exposure.

6. Is the test painful?

The test is not painful. The injection feels like a slight pinch, and mild redness may appear but usually disappears quickly.

How the Tuberculin Skin Test Sample is Collected

Patient Preparation:

The doctor reviews medical history to check for allergies or previous TB-related conditions.
No special preparation is needed, but any known allergies or reactions should be discussed with the doctor.

Subcutaneous Injection (Mantoux):

A small amount (0.1 mL) of purified protein derivative (PPD) is injected under the top layer of skin in the inner forearm.
The needle is inserted at an angle less than 15° to ensure proper subcutaneous injection.

After Injection:

Monitor the area for 48–72 hours.
Return to the doctor for assessment of any swelling or redness.

Causes of Cutaneous TB
Cutaneous TB is a rare skin infection caused by Mycobacterium tuberculosis, the same bacteria responsible for pulmonary TB.

Transmission to the skin:

Direct spread: TB bacteria may travel from lungs or other organs to the skin via blood or lymph (secondary cutaneous TB).
Direct exposure: Bacteria can enter through skin cuts or wounds (primary cutaneous TB).
Internal spread: In immunocompromised individuals, bacteria can travel from inside the body to the skin.

Risk factors:

Weakened immune system (e.g., HIV, diabetes, immunosuppressive drugs)
Direct contact with someone with active TB
Skin injuries or burns
Previous pulmonary TB or TB in other organs

Symptoms of Cutaneous TB

Itching or rash: Small red or brown patches, sometimes itchy.
Ulcers or scales: Patches may develop into open sores with thick crusts or discharge.
Nodules or lumps: Solid lumps under the skin or in nearby lymph nodes.
Slow healing: Skin lesions may persist and not respond to usual infection treatments.
General symptoms: Low-grade fever, fatigue, or gradual weight loss, especially if associated with TB in other organs.

Types of Tuberculin Skin Tests

1. Mantoux Test

Description: Most common and standard TB skin test worldwide.
Procedure: A small amount of PPD is injected under the forearm skin.
Reading: After 48–72 hours, the site is checked for redness or swelling. A raised area indicates immune response, suggesting prior exposure or infection.

2. Tine Test

Description: Less common than Mantoux.
Procedure: Small tools with TB protein are pressed onto the skin to detect a reaction.

Procedure for the Tine PPD Test:

The device, which contains small needles, is pressed against the skin of the arm and left in place to trigger a response.
Results are read after 48–72 hours.

Difference from Mantoux Test:

Less accurate than the Mantoux test.
Often used in specific cases for children.

3. PPD Heaf Test

Description: Previously used in some countries, this test used small needles to inject tuberculin protein under the skin.
Current use: Largely replaced by the Mantoux test due to better accuracy and easier reading.

Why is the Tuberculin Skin Test Performed?
The PPD test is conducted to detect exposure to TB bacteria, whether the infection is active or latent. Main reasons include:

Early detection of latent TB:
- Some people carry TB bacteria without symptoms.
- Helps detect latent infection before it develops into active disease.
- Important for high-risk groups such as:
  - Close contacts of active TB patients
  - Healthcare workers
  - Immunocompromised individuals
Supportive diagnosis of active TB:
- Indicates if the immune system has encountered TB bacteria.
- Diagnosis is confirmed with chest X-rays, sputum analysis, and other tests.
Screening for children, immigrants, or students:
- Required in some countries for school, university entry, or immigration.
Monitoring high-risk individuals:
- For example, people with HIV or those on immunosuppressive therapy.
- Helps doctors decide on preventive treatment.

Who Should Take the PPD Test?

Close contacts of active TB patients:
- Family members, coworkers, or friends who share the same environment.
Healthcare workers or long-term care staff:
- Exposure to patients with active TB increases risk.
Immunocompromised individuals:
- HIV/AIDS patients
- Those on immunosuppressive drugs (e.g., post-transplant, chemotherapy)
- Individuals with immune-affecting diseases like uncontrolled diabetes or cancer
Immigrants from high TB prevalence areas:
- Especially from Southeast Asia, Africa, or Latin America.
Children and infants:
- Living in high-risk environments or in contact with infected individuals.
People with chronic lung disease:
- Asthma or other chronic pulmonary conditions increase risk if exposed.
People with malnutrition or other health conditions:
- Severe malnutrition, anemia, or other health issues increasing susceptibility.
People in crowded or unhealthy environments:
- Refugees, prisons, or shelters with poor ventilation.
Preventive screening before TB prophylaxis:
- Individuals with a positive latent TB test
- Those starting long-term preventive therapy

Side Effects of the Tuberculin Skin Test:
The PPD test is generally very safe. Some mild, temporary side effects may occur:

Common Side Effects:

Redness or swelling at the injection site
- Small raised area usually appears within 48–72 hours and fades in a few days.
Itching or burning sensation
- Can be relieved with a cold compress or mild cream if advised by a doctor.
Mild pain or tenderness
- Typically disappears within 1–2 days.

Rare Side Effects:

Small blister or ulcer at the injection site
- Usually heals on its own; keep the area clean.
Swollen nearby lymph nodes
- Resolves within about two weeks.
Allergic reactions
- Rare; severe reactions require immediate medical attention.

Reading the Mantoux Test Result:

Timing:

Examine the injection site 48–72 hours after PPD injection.
Reading at 72 hours is most accurate; avoid reading after 96 hours.

What is Measured:

Measure the induration (firm swelling) under the skin, not the redness.
Record the diameter in millimeters (mm).

Interpretation:

Patient Group	Induration Size	Interpretation
Healthy, low-risk	< 5 mm	Likely negative
High-risk (e.g., diabetics, HIV)	≥ 5 mm	Possible infection
Medium-risk or travel to TB areas	≥ 10 mm	Likely exposure
Certain medical history or immunocompromised	≥ 15 mm	Strong reaction, likely infection

Important Notes:

Redness alone does not determine positivity.
Induration is interpreted based on patient history and risk factors.
BCG vaccination may cause minor induration (<10 mm) years after vaccination.

Follow-Up Steps:

Positive test: Chest X-ray and possibly additional tests to rule out active TB.
Negative test: High-risk individuals may need repeat testing or a blood IGRA test.

Prevention of Cutaneous and Latent TB:

BCG Vaccination:
- Protects children from severe TB forms; partially protects adults from pulmonary TB.
Avoid exposure to TB bacteria:
- Maintain distance from active TB patients
- Use masks in crowded areas
- Ensure proper ventilation
Early detection and medical monitoring:
- Regular PPD or IGRA testing for high-risk groups
- Early treatment prevents progression and transmission
Healthy lifestyle:
- Balanced diet, vitamins, and minerals
- Regular exercise
- Adequate sleep, avoiding exhaustion
- Avoid smoking and alcohol
Preventive treatment for exposed individuals:
- For people with a positive latent TB test but no symptoms, doctors may prescribe preventive therapy such as isoniazid to reduce the risk of developing active TB.