T66 vs Z77.123
T66 (Radiation sickness, unspecified) compared with Z77.123 (Contact with and (suspected) exposure to radon and other naturally occurring radiation), from the official CMS tabular data. Both may be reported when both conditions are documented (Excludes2).
Can these codes be reported together?
Yes, when both are documented. Z77.123 carries an Excludes2 note covering T66: “radiation sickness NOS (T66)”
Excludes2 marks distinct conditions — both may be reported when both are documented.
Side by side
| T66Radiation sickness, unspecified | Z77.123Contact with and (suspected) exposure to radon and other naturally occurring radiation | |
|---|---|---|
| Billing status | Non-billable header | Billable |
| Classification | S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) | Z00-Z99 — Factors Influencing Health Status and Contact with Health Services (Z00-Z99) |
| Definition | Radiation sickness, unspecified is a non-billable ICD-10-CM category code (T66). | Contact with and (suspected) exposure to radon and other naturally occurring radiation is a billable ICD-10-CM diagnosis code (Z77.123). |
| 7th character | The appropriate 7th character is to be added to code T66 | — |
| Includes | — | contact with and (suspected) exposures to potential hazards to health |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources