A Heaf gun with disposable single use heads is recommended.
The gun injects purified protein derivative equivalent to 100,000 units per ml to the skin over the flexor surface of the left forearm. The test is read between 3 and 10 days later. The injection must not be into sites containing superficial veins.
The reading of the Heaf test is defined by a scale:
- negative - minute puncture scars, no induration
- grade 1 - at least 4 puncture points are indurated
- grade 2 - coalescence of puncture points forming a ring of induration
- grade 3 - extensive induration (5 - 10 mm)
- grade 4 - severe induration (>=10mm); may be central blistering
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.