Table of Contents
How is PPD measured?
TST Basics
- The TST is an intradermal injection of 0.1 ml of tuberculin (PPD) on the inner surface of the forearm. The skin test reaction should be read between 48 and 72 hours after administration.
- The reaction should be measured in millimeters of induration (palpable, raised, hardened area or swelling).
What is a positive PPD test in mm?
PPD Skin test Conversion According to CDC, the repeat PPD Skin test is considered positive if there is ≥ 10 mm induration and the induration is increased by ≥6 mm compared to the previous test. This test interpretation is less sensitive but more specific.
What size is a PPD needle?
Check expiry date on vial and ensure vial contains tuberculin PPD-S (5 TU/0.1 ml). Use a single-dose tuberculin syringe with a short (¼- to ½-inch) 27-gauge needle with a short bevel.
How big is a positive PPD test?
In a healthy person whose immune system is normal, induration greater than or equal to 15 mm is considered a positive skin test. If blisters are present (vesiculation), the test is also considered positive. In some groups of people, the test is considered positive if induration less than 15 mm is present.
How is PPD induration measured?
The induration should be measured across the forearm, perpendicular to the axis between your hand and elbow. Several factors affect how the test is interpreted . An induration of less than 5 millimeters (mm) is considered a negative test result.
What are injection needle sizes?
The length of a needle is listed after the gauge number. For example, 25G ½ refers to a 25 gauge, ½ inch-long needle. Longer needles (½ inch or longer) are commonly used for intramuscular injections, while shorter (shorter than ½ inch) needles are more often used for intravenous injections.
What is the normal range of TB?
| Components | Reference Interval |
|---|---|
| QuantiFERON-TB Gold In-Tube | Negative |
| QuantiFERON-TB1 minus NIL | 0.34 IU/mL or less |
| QuantiFERON-TB2 minus NIL | 0.34 IU/mL or less |
| QuantiFERON MITOGEN minus NIL | No reference interval |
What is borderline TB?
tuberculosis infection. A borderline test result (T-Spot only) also indicates an uncertain likelihood of M. tuberculosis infection. A diagnosis of LTBI requires that TB disease be excluded by medical evaluation.