Procedure
A Heaf gun is used to inject multiple samples of testing serum under the skin at once. The needle points are dipped in tuberculin purified protein derivative (PPD) and pricked into the skin. A Heaf gun with disposable single-use heads is recommended.
The gun injects PPD equivalent to 100,000 units per ml to the skin over the flexor surface of the left forearm in a circular pattern of six. The test is read between two and seven days later. The injection must not be into sites containing superficial veins.
The reading of the Heaf test is defined by a scale:
- Negative - No induration, maybe six minute puncture scars
- Grade 1 - four to six papules (also considered negative)
- Grade 2 - Confluent papules form indurated ring (positive)
- Grade 3 - Central filling to form disc (positive)
- Grade 4 - Disc >10 mm with or without blistering (strongly positive)
Grades 1 and 2 may be the result of previous BCG or avian tuberculosis.
Children who have a grade 3 or 4 reaction require X-ray and follow-up.
For interpretation of the test, see Tuberculosis diagnosis.
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