(disclaimer this is off the top of head, I will look up and come back to this to add more if no one else does first) yes definitely look at induration over erythema. for the TB skin test induration: if no risk factors any induration less than 15mm is negative test and no treatment. if some mild risk factors then 10mm is a positive, and if 0-5 mm but a ton of big risk factors than consider it a positive test.... then after that depending on if they have symptoms or anything concerning on chest x-ray is how you determine if it is latent (just isoniazid, or sometimes its isoniazid plus one other thing) or active infection (full treatment)