Intradermal injection: a complete nursing guide

Intradermal injection is the most technically demanding of the three parenteral routes. The needle enters the skin at a shallow angle — 5 to 15 degrees — into the dermis itself, not below it. Done correctly, the medication has nowhere to go except into the tight, avascular dermal tissue, producing a small raised wheal on the skin surface. Done incorrectly — angle too steep, depth too great — the drug disperses into subcutaneous fat, the wheal fails to form, and the test is invalid.

The primary clinical application is the Mantoux tuberculin skin test (TST), used to screen for latent tuberculosis infection. Secondary uses include allergy skin testing and anergy testing panels. Understanding intradermal injection technique thoroughly is essential for nursing practice and consistently appears on NCLEX.

Quick-reference summary

What intradermal injection is and when it is used

The dermis lies beneath the epidermis and above the subcutaneous layer. It is a dense, fibrous layer of connective tissue with limited vascularity — which is precisely what makes it useful for diagnostic testing. Because drugs absorbed intradermally enter circulation very slowly, a localized immune or inflammatory response at the injection site can be observed and measured without the test substance being rapidly cleared. This characteristic makes intradermal injection the route of choice for:

Tuberculin skin test (Mantoux test): 0.1 mL of purified protein derivative (PPD) is injected into the dermis of the volar forearm. In individuals previously exposed to Mycobacterium tuberculosis, sensitized T lymphocytes mount a delayed-type hypersensitivity reaction, producing measurable induration at the site within 48–72 hours.

Allergy skin testing: Small amounts of specific allergens are introduced intradermally to detect IgE-mediated hypersensitivity. A positive reaction (wheal-and-flare) indicates sensitization to that antigen. This is typically performed by allergists using a panel of multiple antigens along the forearm or back.

Anergy testing: If a patient’s immune system is severely suppressed, a negative TST result may reflect failed immune response (anergy) rather than absence of TB exposure. Anergy is assessed by simultaneously testing with common recall antigens (e.g., Candida, mumps). If no reaction occurs to any antigen, TST results cannot be interpreted as evidence against TB exposure.

Equipment

Gathering the correct equipment before approaching the patient prevents interruptions and ensures the test is performed correctly from the start:

• 1 mL tuberculin syringe — calibrated in 0.01 mL increments; standard syringes do not provide the precision needed
• 26–27 gauge needle, 3/8–5/8 inch length — fine gauge minimizes trauma and keeps the injection superficial
• Tuberculin PPD antigen — 5 tuberculin units (TU) per 0.1 mL is the standard US dose (Aplisol or Tubersol)
• Alcohol wipes (70% isopropyl)
• Gloves (clean, non-sterile)
• Skin marker or pen — some institutions mark the injection site perimeter to assist with return reading
• Ruler calibrated in millimeters — for reading induration at 48–72 hours; a flexible ruler or calipers work best

Do not substitute a standard 1 mL syringe with a different needle length. A longer needle increases the risk of inadvertent subcutaneous injection.

Site selection

The preferred site for intradermal injection is the volar (inner) surface of the forearm, approximately 2–4 fingerwidths (4–6 cm) below the antecubital fossa. The skin here is thin, relatively hairless, lightly pigmented, and lacks significant subcutaneous fat directly under the dermis — all factors that make it ideal for a superficial injection and for reading the resulting reaction.

Avoid the following within the forearm site:

• Visible veins (risk of inadvertent IV injection)
• Areas of skin breakdown, rash, bruising, or scarring (alters tissue response)
• Heavily tattooed areas (pigment obscures reaction reading)
• Bony prominences or tendons

If the volar forearm is not usable (skin condition, extensive scarring), the upper outer arm — below the deltoid insertion — is an acceptable alternative. Document the alternative site in the chart and notify the reading clinician, as site variations are relevant to result interpretation.

Site comparison:

Step-by-step procedure

Before the procedure

1. Verify the order — confirm antigen, dose, and site; check for contraindications (see below).
2. Identify the patient using two identifiers.
3. Screen for prior positive TST or documented BCG vaccination — both affect whether the test should proceed.
4. Perform hand hygiene and don clean gloves.
5. Draw up 0.1 mL of PPD into the tuberculin syringe. Expel any air bubbles carefully — any air in the syringe reduces the volume of antigen delivered and can displace the wheal.

Skin preparation

6. Clean the site with an alcohol wipe using a circular motion, center outward.
7. Allow the alcohol to dry completely — injecting through wet alcohol causes stinging and can introduce alcohol into the dermis, which may alter the reading.

Injection

8. Position the patient’s arm palm-up, forearm resting on a flat surface.
9. Stretch the skin taut with the non-dominant hand by grasping the forearm from below and applying light tension. This flattens the skin and makes needle insertion easier.
10. Hold the syringe with the dominant hand, bevel (opening) facing upward. The needle should be nearly parallel to the skin — 5 to 15 degrees.
11. Insert just the bevel — approximately 3 mm — into the dermis. The needle should be visible through the skin surface. If the needle disappears, it is too deep.
12. Inject 0.1 mL slowly. Resistance will be felt — the dermis is dense and does not accommodate fluid easily. This resistance is expected and confirms correct placement.
13. Observe the wheal forming as you inject. A pale, raised, blister-like elevation — 6 to 10 mm in diameter — should appear at the injection site. The skin may show a peau d’orange (orange peel) texture from the stretched pores.
14. Withdraw the needle at the same angle it entered. Do not massage the site — massage disperses the antigen into subcutaneous tissue and invalidates the test.
15. Do not recap the needle. Activate the safety device and discard into a sharps container immediately.

After the procedure

16. Circle the injection site with a skin marker if institutional policy requires it, to assist the return reader in locating the wheal site at 48–72 hours.
17. Document the time of injection, site, lot number and expiration date of the PPD, and the nurse administering.
18. Instruct the patient when to return for reading (48–72 hours) and to avoid rubbing or applying topical preparations to the site. The patient should also watch for rare severe reactions (anaphylaxis) and know when to seek urgent care.

If no wheal forms

Absence of a wheal indicates the injection entered subcutaneous tissue rather than the dermis. This renders the test invalid and requires repeat injection. The repeat must be administered:

• On the other forearm (not the same site)
• With a new dose of PPD
• With attention to angle correction — the most common cause is an angle greater than 15 degrees

Do not document an absent-wheal injection as a valid TST. Report and repeat per institutional policy.

Reading the Mantoux TST

The Mantoux test must be read between 48 and 72 hours after injection. Reading before 48 hours misses the peak delayed hypersensitivity response; reading after 72 hours underestimates induration as the reaction begins to resolve. If a patient cannot return in this window, the test must be repeated.

What to measure: induration, not erythema

This is the most common error students and new nurses make. Measure induration — the palpable, firm, raised area — not the surrounding redness (erythema). Erythema alone without induration is not a positive result.

How to measure:

1. Palpate the site with the fingertips to identify the boundaries of the firm, raised area.
2. Using a flexible ruler or calipers, measure the induration across the transverse axis (perpendicular to the long axis of the forearm) at its widest point.
3. Record the measurement in millimeters. Record 0 mm if no induration is present — do not write “negative.”

Interpretation thresholds

The same millimeter measurement may be positive or negative depending on the patient’s risk category. There is no universal cut-off. The CDC defines three interpretation thresholds based on prior exposure risk and immune status:

A positive TST does not diagnose active TB. It indicates that the person has been infected with M. tuberculosis at some point — either recently or in the past. Active disease requires chest X-ray and clinical evaluation. A positive TST in a person with no symptoms and a normal chest X-ray suggests latent TB infection (LTBI), which may be treated with a course of isoniazid to prevent future reactivation.

Booster effect and two-step testing

Some individuals — particularly older adults and those vaccinated with BCG decades ago — have a waned immune response to PPD. A first TST may read negative even in someone with prior TB exposure, because the initial test does not elicit a measurable reaction. However, that first exposure to PPD can restimulate (boost) the immune memory, so that a second TST administered 1–3 weeks later produces a positive reaction.

This is the booster effect, and it creates a diagnostic problem: the positive second test might be interpreted as a new conversion (suggesting recent infection), when in fact it reflects remote infection or BCG vaccination.

Two-step testing is used in settings where serial TST monitoring will be performed (healthcare workers, long-term care residents). The process:

1. Administer the first TST.
2. Read at 48–72 hours.
3. If negative, administer a second TST 1–3 weeks later.
4. Read the second TST at 48–72 hours.
5. If the second test is positive, this is attributed to the booster effect (remote exposure), not new infection.
6. This two-step result becomes the baseline for future serial testing. Future conversions are then measured against this baseline.

If a single-step TST is used as baseline and is negative, a subsequent positive result would be classified as a TST conversion — a ≥10 mm increase from baseline — and would require further evaluation regardless of BCG history.

Contraindications

Prior documented positive TST: Repeat testing in a known positive patient is unnecessary and risks a severe local reaction (ulceration, necrosis). If a patient reports a prior positive TST, verify with documentation, obtain the original millimeter reading, and do not repeat the test. Interferon-gamma release assays (IGRAs, e.g., QuantiFERON-TB Gold) are an alternative that carry no such risk.

Documented active TB: Testing adds no diagnostic value.

Severe blistering skin conditions affecting the forearm site (pemphigus, severe eczema): use an alternative site or IGRA.

BCG vaccination: BCG (Bacille Calmette-Guérin) vaccine is routinely administered in many countries outside the US. BCG vaccination can cause a false-positive TST, particularly if the vaccine was given after infancy. The IGRA test (blood-based) is not affected by BCG and is preferred for BCG-vaccinated individuals. However, BCG vaccination is not a contraindication to TST administration — it is a consideration in interpreting results. Document BCG history and discuss with the ordering provider before proceeding.

Pregnancy: The TST is considered safe in pregnancy. The CDC does not list pregnancy as a contraindication.

Common mistakes to avoid

Injecting at the wrong angle: IM and SQ injections use 90° and 45° angles respectively. An intradermal injection at 45° or 90° deposits antigen into subcutaneous tissue — the wheal will not form, and the test is invalid. The angle must be 5–15 degrees, with the needle nearly parallel to the skin surface.

Bevel facing down: With the bevel down, the needle opening faces the dermis and the injection is deflected upward, reducing accuracy of depth and making wheal formation less reliable. Always inject bevel up.

Injecting too quickly: Rapid injection into dense dermal tissue causes the fluid to tear through the tissue plane rather than form a clean wheal. Slow, steady pressure produces the best bleb.

Massaging the site: Any massage after injection disperses the antigen and invalidates the test. Inform the patient explicitly before you withdraw the needle.

Measuring erythema instead of induration: The ring of redness (erythema) surrounding the wheal is not a diagnostic finding. Only the firm, palpable, raised induration counts. Students who report “the site is red” without palpating for firmness are measuring the wrong thing.

Reading outside the 48–72 hour window: Reading too early (24 hours) misses the full immune response. Reading late (96+ hours) underestimates induration. Neither reading is valid for documentation.

Missing the two-step indication: In healthcare workers or long-term care settings getting a baseline TST, a single-step protocol sets a false negative baseline that will classify future boosted reactions as new conversions. Follow institutional policy for two-step testing in serial monitoring programs.

Intradermal vs. other injection routes

Understanding intradermal technique is easier when contrasted with the other parenteral routes. For a detailed comparison of IM and SQ techniques, see the injection techniques nursing guide. For IM-specific technique including the Z-track method — used when irritating medications must be sealed in muscle tissue — see Z-track method. For venipuncture — the technical skill most related to needle handling and site assessment — see venipuncture nursing.

The key distinctions for NCLEX:

NCLEX high-yield points

Needle angle: 5–15 degrees is the only correct answer for intradermal injection. Distractors include 45° (subcutaneous) and 90° (intramuscular). Know which angle belongs to which route.

“Wheal” vs. “bleb”: Both terms refer to the pale, raised bubble that forms at the injection site. Both are used interchangeably in nursing literature. Expect both terms on NCLEX questions.

Bevel position: Always upward (bevel up) for intradermal injection. Bevel-down insertion reduces accuracy.

Reading the TST: 48–72 hours — not 24 hours, not 1 week. Read induration only. Erythema alone is never a positive result.

Interpretation thresholds: ≥5 mm (HIV/immunocompromised/recent contact), ≥10 mm (high-risk groups including healthcare workers, immigrants, and correctional facilities), ≥15 mm (low-risk adults). These are the numbers NCLEX tests.

No massage: After injection of any diagnostic skin test, do not massage. This appears in NCLEX questions as a post-procedure instruction.

No repeat testing in known positives: A prior positive TST is a contraindication to repeat testing — document and use IGRA instead.

Two-step testing: Used for baseline testing in healthcare workers and residents of congregate settings where serial monitoring will occur. First negative result → repeat in 1–3 weeks → if second result positive, this is the baseline (booster, not conversion).

Key takeaways

Intradermal injection is a precision skill. The difference between a valid result and an invalid one comes down to a few degrees of needle angle, a single motion of massage or no massage, and a 24-hour difference in when the reading is performed. The Mantoux TST has been the standard for latent TB detection for decades, and nurses are the clinicians most often administering and reading it.

Master the 5–15 degree angle. Confirm your wheal every time. Measure induration at 48–72 hours using a ruler. Know the three interpretation thresholds by heart. These four elements cover the vast majority of intradermal injection questions in both clinical practice and on NCLEX.