Tuberculin tine tests: effect of variations in dried tuberculin coating.

The dried tuberculin coatings of the tines of multiple puncture disposable tests have been found to vary in thickness and distribution. Tines which are thinly and uniformly coated at their distal 0.6-0.8 mm produce consistent responses in tuberculin positive subjects. Where the tuberculin coating is thickened and retracted from the tips, a significant number of negative responses occur in tuberculin positive subjects. Observations of tines under an electron microscope after application have shown loss of tuberculin coating from the distal 0.6-0.8 mm only. Application of tines through Indian ink placed on the skin of cadavers has confirmed that times penetrate the dermis to a maximum depth of 0.6 mm.