Is G21 a billable ICD-10-CM code?

No. G21 is a non-billable header code. Code to a higher level of specificity using one of its child codes.

Where does G21 sit in the tabular list?

Diseases of the nervous system (G00-G99), in the block Extrapyramidal and movement disorders (G20-G26).

What cannot be coded together with G21?

G21 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.

G21

G21 — Secondary parkinsonism

Non-billable headerICD-10-CM

G21 is a non-billable header ICD-10-CM code for secondary parkinsonism. It cannot be billed on its own: choose one of the more specific child codes below.

Excludes1 — never code together

These conditions cannot occur together. Billing both on the same encounter is a denial.

Huntington's disease (G10)
neurocognitive disorder with Lewy bodies (G31.83)
Shy-Drager syndrome (G90.3)
syphilitic Parkinsonism (A52.19)

Other codes that can never be billed with G21

These codes carry an Excludes1 note pointing at G21. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading G21 alone.

G20.CParkinsonism, unspecified
G21.0Malignant neuroleptic syndrome
G21.11Neuroleptic induced parkinsonism

Risk adjustment

G21 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.

Code to one of these instead G21

7 child codes. Green means billable.

Questions about G21

Is G21 a billable ICD-10-CM code?: No. G21 is a non-billable header code. Code to a higher level of specificity using one of its child codes.
Where does G21 sit in the tabular list?: Diseases of the nervous system (G00-G99), in the block Extrapyramidal and movement disorders (G20-G26).
What cannot be coded together with G21?: G21 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.