I21.B — Myocardial infarction with coronary microvascular dysfunction

BillableMCC

Is I21.B billable?

Yes — I21.B is billable for FY2027. I21.B is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. I21.B may be submitted for encounters from October 1, 2026 through September 30, 2027.

I21.B at a glance

Code	I21.B
Description	Myocardial infarction with coronary microvascular dysfunction
Billable	Yes
Code set	ICD-10-CM FY2027
Valid for encounters	October 1, 2026 – September 30, 2027

Which MS-DRGs does I21.B group to?

I21.B sits in MDC 05 and helps define the logic of 6 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.

280Acute Myocardial Infarction, Discharged Alive with MCCmedical
281Acute Myocardial Infarction, Discharged Alive with CCmedical
282Acute Myocardial Infarction, Discharged Alive without CC/MCCmedical
283Acute Myocardial Infarction, Expired with MCCmedical
284Acute Myocardial Infarction, Expired with CCmedical
285Acute Myocardial Infarction, Expired without CC/MCCmedical

As a secondary diagnosis, I21.B is a major complication or comorbidity (MCC), which can move a stay into a higher-paying DRG.

How is I21.B listed in the Alphabetic Index?

These are the routes through the Alphabetic Index that lead to I21.B. They show the wording a clinician may have documented, which often differs from the Tabular description.

Dysfunction › coronary microvascular › with › myocardial infarction
Infarct, infarction › myocardium, myocardial › with › coronary microvascular disease
Infarct, infarction › myocardium, myocardial › with › coronary microvascular dysfunction
Infarct, infarction › myocardium, myocardial › with › nonobstructive coronary arteries [MINOCA] with microvascular disease
Disease, diseased › coronary › microvascular › with › myocardial infarction

Inclusion terms

Alternative wording in documentation that is classified to I21.B.

Myocardial infarction with coronary microvascular disease
Myocardial infarction with nonobstructive coronary arteries [MINOCA] with microvascular disease

Use additional code — inherited from I21

Report an additional code alongside I21.B to fully describe the condition. I21.B is sequenced first.

code, if applicable, to identify:
exposure to environmental tobacco smoke (Z77.22)
history of tobacco dependence (Z87.891)
occupational exposure to environmental tobacco smoke (Z57.31)
status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
tobacco dependence (F17.-)
tobacco use (Z72.0)

Excludes2 — not included here — inherited from Chapter 9

The conditions below are not part of I21.B, but a patient may have both at the same time. When documentation supports it, I21.B and the excluded code may both be reported.

certain conditions originating in the perinatal period (P04-P96)
certain infectious and parasitic diseases (A00-B99)
complications of pregnancy, childbirth and the puerperium (O00-O9A)
congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
endocrine, nutritional and metabolic diseases (E00-E88)
injury, poisoning and certain other consequences of external causes (S00-T88)
neoplasms (C00-D49)
symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
systemic connective tissue disorders (M30-M36)
transient cerebral ischemic attacks and related syndromes (G45.-)

Excludes2 — not included here — inherited from I21

The conditions below are not part of I21.B, but a patient may have both at the same time. When documentation supports it, I21.B and the excluded code may both be reported.

old myocardial infarction (I25.2)
postmyocardial infarction syndrome (I24.1)
subsequent type 1 myocardial infarction (I22.-)

Code also — inherited from I20-I25

Two codes may be needed to describe the condition fully. Whether I21.B is sequenced first depends on the reason for the encounter.

the presence of hypertension (I10-I1A)

How long has I21.B existed?

I21.B first appears in FY2024.

Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.