The depth of a burn is judged on its appearance, texture and sensitivity. It can be difficult to distinguish between erythema and superficial partial thickness burns particularly if the patient is seen soon after injury when blister formation is minimal. The presence of thrombosed capillaries in burned skin is pathognomic of a full thickness burn. Flash burns whether electrical or from vapour are usually very superficial but are often mistaken as deep burns because of the presence of carbon-staining. For this reason, it is helpful to clean the burned area prior to examination.
Sensory testing is difficult under any circumstances.
Pin-prick testing is often unnecessary and is inappropriate in children. If performed, it is preferable initially to stroke gently the burned area with a sterile needle, having familiarised the patient with the test on an unburned area. Accurate assessment burn-depth is particularly difficult in the early hours after injury. Re-examination after 24 hours may be useful as the signs are well established by this time allowing definitive decisions to be made about management. The likely depth of burn also depends on the area burned because the thickness of skin of the hand varies considerably.