T56.1X4A (Toxic effect of mercury and its compounds, undetermined, initial encounter) compared with T56.1X4D (Toxic effect of mercury and its compounds, undetermined, subsequent encounter), from the official CMS tabular data. T56.1X4A and T56.1X4D code the same injury at a different phase of treatment.
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
Same injury, other encounter phase. T56.1X4A and T56.1X4D 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.
| T56.1X4AToxic effect of mercury and its compounds, undetermined, initial encounter | T56.1X4DToxic effect of mercury and its compounds, undetermined, subsequent encounter | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) |
| Definition | Toxic effect of mercury and its compounds, undetermined, initial encounter is a billable ICD-10-CM diagnosis code (T56.1X4A). | Toxic effect of mercury and its compounds, undetermined, subsequent encounter is a billable ICD-10-CM diagnosis code (T56.1X4D). |
| 7th character | The appropriate 7th character is to be added to each code from category T56 | The appropriate 7th character is to be added to each code from category T56 |
| Includes | toxic effects of fumes and vapors of metals toxic effects of metals from all sources, except medicinal substances | toxic effects of fumes and vapors of metals toxic effects of metals from all sources, except medicinal substances |
| Use additional code | code to identify any retained metal foreign body, if applicable (Z18.0-, T18.1-) code(s): for all associated manifestations of toxic effect, such as: respiratory conditions due to external agents (J60-J70) | code to identify any retained metal foreign body, if applicable (Z18.0-, T18.1-) code(s): for all associated manifestations of toxic effect, such as: respiratory conditions due to external agents (J60-J70) |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources