Tuberculin Skin Test: Revisiting the Reading Technique

Tuberculin Skin Tests (TST) are widely used but its utility is compromised by variations in reading the reactions by different observers, as studies over time have consistently shown that health care providers do not always follow established recommendations. To help ensure consistency among TST readers, Centers for Disease Control and Prevention (CDC), Atlanta, USA recommends that the induration following administration of a TST must be measured transverse to long axis of the forearm. Existing literature on measurement of delayed skin test responses have all examined the advantage of using the pen versus the palpation technique for measuring induration, and to the best of our knowledge, none have factored in the role of superficial lymphatics that possibly can influence the vertical diameter of the induration following a TST. Accurate measurement of a TST forms an important element in the continuum of standard of care between administration of a TST and its correct interpretation, and errors in interpretation can lead to institution of inappropriate therapy. It is hoped that this mini-review provides a logical insight based on best available evidence into the possible role of superficial lymphatics in influencing the vertical diameter of the induration along the long axis of the forearm thereby also reinforcing CDC's recommendation for measuring the induration of a positive TST transverse to the long axis of the forearm.