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T65.821A vs T65.821D

T65.821A (Toxic effect of harmful algae and algae toxins, accidental (unintentional), initial encounter) compared with T65.821D (Toxic effect of harmful algae and algae toxins, accidental (unintentional), subsequent encounter), from the official CMS tabular data. T65.821A and T65.821D code the same injury at a different phase of treatment.

Relationship

Review

Encounter relationship

T65.821A
Initial encounter
Toxic effect of harmful algae and algae toxins, accidental (unintentional), initial encounter
↔
T65.821D
Subsequent encounter
Toxic effect of harmful algae and algae toxins, accidental (unintentional), 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. T65.821A and T65.821D 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

T65.821AToxic effect of harmful algae and algae toxins, accidental (unintentional), initial encounterT65.821DToxic effect of harmful algae and algae toxins, accidental (unintentional), subsequent encounter
Billing statusBillableBillable
ClassificationS00-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)
DefinitionToxic effect of harmful algae and algae toxins, accidental (unintentional), initial encounter is a billable ICD-10-CM diagnosis code (T65.821A).Toxic effect of harmful algae and algae toxins, accidental (unintentional), subsequent encounter is a billable ICD-10-CM diagnosis code (T65.821D).
7th characterThe appropriate 7th character is to be added to each code from category T65The appropriate 7th character is to be added to each code from category T65
Includes
Toxic effect of harmful algae and algae toxins NOS
Toxic effect of harmful algae and algae toxins NOS
Use additional code
code(s):
for all associated manifestations of toxic effect, such as: respiratory conditions due to external agents (J60-J70)
personal history of foreign body fully removed (Z87.821)
code(s):
for all associated manifestations of toxic effect, such as: respiratory conditions due to external agents (J60-J70)
personal history of foreign body fully removed (Z87.821)
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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