Blister (nonthermal) of unspecified ear, initial encounter

This code signifies a non-burn-related fluid-filled lesion on an unspecified ear. It indicates the initial presentation or treatment of such a blister, which may arise from friction, pressure, or other non-thermal trauma.

Use this code for a patient presenting with a newly diagnosed blister on the ear where the cause is explicitly documented as non-thermal, and the specific ear (left or right) is not identified. Documentation should clearly state "blister," "nonthermal," and "ear."

• Ensure documentation specifies "nonthermal" to differentiate from burn blisters.
• If the specific ear (left or right) is documented, use the more precise codes S00.421A (right) or S00.422A (left).
• This "A" suffix indicates an initial encounter for active treatment; use subsequent encounter codes for follow-up care.