Tuberculin PPD RT: Uses, Dosage & Side Effects

What Is Tuberculin PPD RT and What Is It Used For?

Tuberculin PPD RT is a purified protein derivative used as a skin test (Mantoux test) to diagnose whether a person has been infected with the bacteria that cause tuberculosis (TB). It is intended exclusively for diagnostic use and is not a vaccine or therapeutic agent.

Tuberculin PPD RT 23, manufactured by AJ Vaccines A/S, is one of the most widely used tuberculin preparations worldwide for the detection of latent tuberculosis infection (LTBI). The test works by exploiting the body's delayed-type hypersensitivity (Type IV) immune response. When a small quantity of purified mycobacterial proteins is injected into the superficial layers of the skin, individuals who have previously been exposed to Mycobacterium tuberculosis will mount an immune response that produces a visible and palpable area of induration at the injection site.

The tuberculin skin test (TST), also referred to as the Mantoux test, has been a cornerstone of tuberculosis screening programmes globally for over a century. The World Health Organization (WHO) recognises it as a key diagnostic tool, particularly in settings where interferon-gamma release assays (IGRAs) are not readily available. The test is used for screening individuals who may have been exposed to TB, evaluating patients with symptoms suggestive of tuberculosis, and as part of pre-vaccination assessment before BCG administration in some countries.

It is important to understand that a positive tuberculin skin test does not necessarily mean a person has active tuberculosis disease. A positive result indicates that the individual's immune system has been sensitised to mycobacterial antigens, which may result from infection with M. tuberculosis, prior BCG vaccination, or exposure to non-tuberculous mycobacteria. Further diagnostic evaluation, including chest radiography and sputum analysis, is required to distinguish between latent infection and active disease.

How does the tuberculin skin test work?

The test relies on cell-mediated immunity. When a person is exposed to M. tuberculosis (through infection or BCG vaccination), their T-lymphocytes become sensitised to mycobacterial antigens. Upon subsequent exposure to tuberculin PPD injected into the skin, these memory T-cells migrate to the injection site and release cytokines, including interferon-gamma, which recruit other immune cells. This cascade produces the characteristic induration — a firm, raised area of skin that can be felt and measured — within 48 to 72 hours.

The degree of induration correlates with the strength of the immune response. A larger induration generally suggests a more robust immunological memory to mycobacterial antigens, which is more likely to reflect true TB infection rather than cross-reactivity from BCG vaccination or environmental mycobacteria exposure.

What Should You Know Before Using Tuberculin PPD RT?

Do not use Tuberculin PPD RT if you have a known allergy to tuberculin or have previously experienced severe local reactions (blistering or ulceration) to tuberculin products. Inform your healthcare provider about recent vaccinations, immunosuppressive medications, and any current illnesses before the test.

Contraindications

Tuberculin PPD RT should not be used in the following circumstances:

• Allergy to tuberculin PPD: If you are allergic to tuberculin purified protein derivative (PPD) RT 23 or any of the excipients in the formulation
• Previous severe local reactions: If you have previously experienced severe local reactions to tuberculin products, such as blistering, vesiculation, or ulceration at the injection site

There are no absolute age-related contraindications. The test can be administered to neonates, children, adults, and elderly patients. However, interpretation of results must always account for the patient's clinical context, including immune status and vaccination history.

Warnings and Precautions

Before undergoing the tuberculin skin test, inform your healthcare provider about the following:

• Recent tuberculin testing: If you have had a tuberculin skin test within the past 12 months, as repeated testing can cause a booster effect that may amplify subsequent results
• Recent vaccination: If you have received any vaccination within the past 4–6 weeks, particularly BCG, measles, mumps, or other live virus vaccines, as these may affect the test result
• Immunosuppressive conditions: Conditions such as HIV/AIDS, diabetes mellitus, chronic renal failure, cancer, or sarcoidosis can suppress the tuberculin response and lead to false-negative results
• Immunosuppressive medications: Corticosteroids, biological agents (including TNF-alpha inhibitors), chemotherapy, or other immunosuppressive drugs may reduce the skin test response
• Recent viral infections: Infections such as measles, mumps, infectious mononucleosis, chickenpox, or influenza within the preceding months may temporarily suppress tuberculin reactivity

Drug Interactions

While Tuberculin PPD RT does not interact with medications in the traditional pharmacological sense, several drugs and conditions can influence the accuracy of the test result:

Pregnancy and Breastfeeding

The tuberculin skin test can be safely performed during pregnancy and breastfeeding. Tuberculin PPD RT contains purified protein derivative, not live organisms, and there are no known risks to the mother, fetus, or nursing infant. In fact, if tuberculosis infection is suspected during pregnancy, prompt testing is recommended because untreated active TB poses significant risks to both mother and baby, including premature birth, low birth weight, and neonatal TB.

The WHO and major international guidelines support tuberculin skin testing in pregnant women when clinically indicated. Delaying diagnosis and treatment of tuberculosis during pregnancy is generally considered a greater risk than performing the skin test.

Driving and Operating Machinery

No effects on the ability to drive or use machinery have been observed with Tuberculin PPD RT. The test involves a minor intradermal injection and does not contain any substances that would impair cognitive function or motor skills.

What Is the Correct Dosage of Tuberculin PPD RT?

The standard dose is 0.1 mL (containing 2 tuberculin units) injected intradermally into the middle third of the inner forearm. The same dose is used for both adults and children. The test must be administered and read by a trained healthcare professional.

Tuberculin PPD RT is administered using the Mantoux technique, which involves a precise intradermal injection. The procedure must be performed by a healthcare professional trained in the technique, as incorrect administration (such as subcutaneous injection) will invalidate the results. The dose is the same for all age groups and does not require adjustment based on body weight or renal or hepatic function.

Adults

Children

Elderly

Administration Technique

Correct intradermal injection technique is critical for accurate test results. The detailed procedure is as follows:

1. Draw up exactly 0.1 mL of Tuberculin PPD RT into a 1 mL graduated syringe fitted with a 25G or 26G short bevelled needle
2. Select the injection site on the middle third of the inner forearm — avoid injecting near the wrist or elbow, as the reaction may be weakened in these areas
3. Stretch the skin slightly and hold the needle nearly parallel to the skin surface with the bevel facing upward
4. Insert the needle tip into the superficial layers of the dermis — the needle should be visible through the epidermis during insertion
5. Inject 0.1 mL slowly; a pale wheal of 8–10 mm in diameter should form, which disappears after approximately 10 minutes
6. If no wheal forms, the injection has been administered too deeply (subcutaneously) and must be repeated on the other arm or at least 4 cm from the original site on the same arm

If the Test Must Be Repeated

If the injection was not performed correctly (no wheal formation), the test must be repeated immediately. The second injection should be given on the other arm or at a distance of at least 4 cm from the first injection site. National guidelines on the Mantoux tuberculin skin test should be followed for all procedural aspects.

How Are Tuberculin PPD RT Test Results Interpreted?

The test result is read 48–72 hours after injection by measuring the induration (firm swelling) in millimeters across the forearm. A result of 0–5 mm is negative, 6–14 mm is positive, and 15 mm or more is strongly positive. Only the induration is measured, not the surrounding redness.

Accurate reading and interpretation of the tuberculin skin test requires training and experience. The reaction manifests as a flat, irregularly shaped, slightly raised area of induration (hardening) surrounded by erythema (redness). Only the induration is clinically significant and should be measured. The diameter is recorded in millimeters, measured transversely (across) the long axis of the forearm using a transparent, flexible plastic ruler.

It is important to note that the interpretation thresholds may vary by country and clinical context. Some guidelines, particularly from the CDC in the United States, use different cut-off values based on the patient's risk factors:

• ≥5 mm is considered positive in HIV-positive individuals, recent contacts of active TB cases, persons with fibrotic changes on chest X-ray consistent with prior TB, organ transplant recipients, and persons who are immunosuppressed
• ≥10 mm is considered positive in recent immigrants from high-prevalence countries, injection drug users, residents and employees of high-risk congregate settings, healthcare workers, and children under 4 years of age
• ≥15 mm is considered positive in persons with no known risk factors for TB

Causes of a positive result

A positive tuberculin skin test indicates that the individual's immune system has been sensitised to mycobacterial antigens. This can occur for several reasons:

• Infection with M. tuberculosis complex: Including M. tuberculosis, M. bovis, M. africanum, M. microti, or M. tuberculosis ssp. caprae
• Non-tuberculous mycobacteria (NTM): Cross-reactivity with environmental mycobacteria can produce a positive result, typically with smaller indurations
• Prior BCG vaccination: BCG-vaccinated individuals typically become tuberculin-positive 4–8 weeks after vaccination, though this reactivity generally wanes over time

Reactions of 15 mm or more are unlikely to be caused by BCG vaccination alone or environmental mycobacterial exposure. In such cases, true TB infection should be strongly suspected, and further investigation including chest radiography and, where appropriate, sputum analysis or IGRA testing should be pursued.

What Are the Side Effects of Tuberculin PPD RT?

Most side effects are mild and localised, including pain, itching, and irritation at the injection site. Serious side effects such as anaphylaxis are extremely rare (fewer than 1 in 10,000). Fever, swollen lymph nodes, and skin necrosis are uncommon to rare.

Like all medicinal products, Tuberculin PPD RT can cause side effects, although not everyone will experience them. The vast majority of adverse reactions are mild and confined to the injection site. Serious systemic reactions are exceptionally rare. Healthcare professionals should have appropriate resuscitation equipment available when administering the test, as with any injectable medicinal product.

Most injection-site reactions are an expected part of the test mechanism. The development of induration (hardening) and erythema (redness) at the injection site is a normal immune response and is what healthcare providers measure to interpret the test result. This expected reaction should not be confused with an adverse effect. The induration typically resolves within days of the reading.

In individuals with a very strong immune response to mycobacterial antigens (for example, those with active or recently treated TB), the local reaction may be more pronounced, potentially including vesiculation or superficial necrosis. While these reactions are uncomfortable, they are generally self-limiting and resolve without specific treatment. A strongly positive reaction of this nature provides valuable diagnostic information.

How Should Tuberculin PPD RT Be Stored?

Store in a refrigerator at 2°C–8°C in the original packaging to protect from light. Use immediately after opening. Do not freeze. Keep out of the reach of children.

Proper storage of Tuberculin PPD RT is essential to maintain the potency and accuracy of the diagnostic agent. Incorrect storage can lead to decreased activity, which may result in falsely weakened skin test reactions and potentially missed diagnoses of tuberculosis infection.

• Temperature: Store in a refrigerator at 2°C to 8°C (36°F to 46°F). Do not freeze.
• Light protection: Store in the original packaging to protect from light, as the product is photosensitive
• After opening: Tuberculin PPD RT should be used immediately after opening. If not used immediately, it may be stored for a maximum of 24 hours at 2°C–8°C, though the user is responsible for ensuring appropriate storage conditions during this period
• Expiry date: Do not use after the expiry date printed on the packaging. The expiry date refers to the last day of the indicated month
• Children: Keep out of the sight and reach of children
• Disposal: Do not dispose of via household waste or wastewater. Return unused product to a pharmacy or healthcare facility for proper disposal in accordance with local regulations

Tuberculin PPD RT does not contain live material. However, it is a biological product and should be handled in accordance with standard procedures for injectable medicinal products. Healthcare facilities should maintain cold-chain integrity from receipt through administration.

What Does Tuberculin PPD RT Contain?

The active ingredient is Tuberculin Purified Protein Derivative (PPD) RT 23. Each 0.1 mL dose of the 2 TU formulation contains 0.04 micrograms of PPD RT 23. Excipients include phosphate buffers, sodium chloride, potassium hydroxyquinoline sulfate, polysorbate 80, and water for injections.

Active ingredient

The active substance is tuberculin purified protein derivative (PPD) RT 23. One dose (0.1 mL) of Tuberculin PPD RT 23 at 2 TU strength contains 0.04 micrograms of PPD RT 23. The higher-strength formulation (10 TU) contains 0.2 micrograms per 0.1 mL dose, though the 2 TU strength is the standard for clinical use.

Inactive ingredients (excipients)

• Disodium phosphate dihydrate — buffering agent to maintain pH stability
• Potassium dihydrogen phosphate — buffering agent
• Sodium chloride — isotonicity agent to match physiological saline concentration
• Potassium hydroxyquinoline sulfate — preservative
• Polysorbate 80 — surfactant to prevent protein adsorption to container surfaces
• Water for injections — solvent

The product contains less than 1 mmol (39 mg) of potassium and less than 1 mmol (23 mg) of sodium per dose, making it essentially potassium-free and sodium-free. This is not clinically relevant for the vast majority of patients.

Physical appearance and packaging

Tuberculin PPD RT 23 is a clear, colourless to slightly yellowish solution for injection. It is supplied in glass vials containing 1.5 mL of solution (sufficient for approximately 15 individual doses of 0.1 mL each). The product is available in pack sizes of 1 or 10 vials, although not all pack sizes may be marketed in every country.

Frequently Asked Questions