T23.431A vs T23.431D

T23.431A (Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, initial encounter) compared with T23.431D (Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, subsequent encounter), from the official CMS tabular data. T23.431A and T23.431D code the same injury at a different phase of treatment.

Relationship

Review

Encounter relationship

T23.431A

Initial encounter

Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, initial encounter

↔

T23.431D

Subsequent encounter

Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, subsequent encounter

Same underlying diagnosis, different encounter phase.

The 7th character records the phase of care for the encounter being coded, so a single encounter takes one of these characters, not several. Review whether both phases belong on the same episode of care.

Source: ICD-10-CM Official Guidelines, Section I.C.19.a

Can these codes be reported together?

Same injury, other encounter phase. T23.431A and T23.431D code the same injury at a different phase of treatment, set by the 7th character.

The 7th character records the type of care given at the encounter being coded (ICD-10-CM Official Guidelines, Section I.C.19.a), so one encounter takes one of these, not both.

Side by side

	T23.431ACorrosion of unspecified degree of multiple right fingers (nail), not including thumb, initial encounter	T23.431DCorrosion of unspecified degree of multiple right fingers (nail), not including thumb, subsequent encounter
Billing status	Billable	Billable
Classification	S00-T88 — Injury, poisoning and certain other consequences of external causes	S00-T88 — Injury, poisoning and certain other consequences of external causes
Definition	Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, initial encounter is a billable ICD-10-CM diagnosis code (T23.431A).	Corrosion of unspecified degree of multiple right fingers (nail), not including thumb, subsequent encounter is a billable ICD-10-CM diagnosis code (T23.431D).
7th character	The appropriate 7th character is to be added to each code from category T23	The appropriate 7th character is to be added to each code from category T23
Includes	burns and corrosions of first degree [erythema] burns and corrosions of second degree [blisters][epidermal loss] burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss]	burns and corrosions of first degree [erythema] burns and corrosions of second degree [blisters][epidermal loss] burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss]
Use additional code	external cause code to identify place (Y92) code from category T31 or T32 to identify extent of body surface involved	external cause code to identify place (Y92) code from category T31 or T32 to identify extent of body surface involved
Code first	(T51-T65) to identify chemical and intent	(T51-T65) to identify chemical and intent

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Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources