Reading a TB Skin Test

This video is for those learning how to read a TB skin test and is for educational purposes only. Clips from the TB Services for …

Reading a TB Skin Test/a>

within 48 to 72 hours a patient will return to have their tb skin test read inspect the tst site in a well-lit room the site may have some erythema or redness but this should not be measured as you are looking for a raised formation or in duration no injuriation indicates a negative skin test using a light gentle motion sweep the fingertips over the surface of the forearm in a two inch diameter in all four directions to locate the margins or edges of induration if induration is present use a zigzag feather-like touch over the area to outline the margins of induration be careful not to confuse a margin of induration with a margin of muscle on the forearm to check this raise the patient’s arm to a 45 degree angle and palpate again the diameter of the induration is measured across the forearm to mark the edges of the induration move the fingertips towards the induration rest one fingertip firmly against the indirection margin border mark lightly with a fine dot at the widest edge of the induration repeat the procedure from the other side of the patient’s forearm if the margin is not equally clear all the way around the induration palpate around the induration from the easily felt margin to the not so easily felt margin take the tb skin test caliper ruler and place the zero zero millimeter line inside the left dot edge and read the ruler line to the inside of the right dot edge this will be your measurement to millimeters of the in duration mark and measure the longest diameter across the forearm a five millimeter reaction is considered positive when there has been a recent contact or if the patient’s amino suppressed 10 millimeters or greater is considered positive otherwise reactions to the skin test will vary there is redness and swelling in this reaction but there is no induration this is a very large reaction with blistering swelling and redness make sure to record blistering even if no induration is present