ICD-10 code M30.3: Kawasaki disease coding guide

Key Takeaways

ICD-10 code M30.3 is the billable diagnosis code for mucocutaneous lymph node syndrome, commonly called Kawasaki disease

M30.3 is valid for FY2026 (October 1, 2025 through September 30, 2026) and submittable on CMS-1500 and UB-04 claim forms

Classic Kawasaki disease requires fever lasting 5 or more days plus at least 4 of 5 clinical features. Incomplete presentations need additional workup before coding

Practice management software like Pabau supports accurate ICD-10 code entry and documentation workflows for pediatric and specialty practices

ICD-10 code M30.3 is the billable diagnostic code for Kawasaki disease, an acute inflammatory illness that shows up almost exclusively in young children. Coders run into trouble with it more often than expected, since Kawasaki’s fever, rash, and swollen glands can look like several other pediatric illnesses before the full picture emerges.

Getting the code right, and the documentation behind it, matters both clinically and financially.

ICD-10 code M30.3 at a glance

M30.3 is classified under M30, Polyarteritis nodosa and related conditions, within the M00-M99 musculoskeletal and connective tissue disease chapter of the CDC/NCHS ICD-10-CM tabular list. The table below captures every field a coder or biller needs at a glance.

What is Kawasaki disease? Clinical overview

Kawasaki disease is an acute systemic vasculitis that primarily strikes children under five years of age. It inflames medium-sized blood vessels throughout the body, not just the skin or lymph nodes. That’s why the WHO ICD-10 classification places it inside systemic connective tissue disorders.

Left untreated, meaning without a prompt IV immunoglobulin infusion, coronary artery aneurysm can develop in up to 25% of affected children. That’s why prompt diagnosis, and the accurate documentation and coding that support it, both matter.

The condition is the leading cause of acquired heart disease in children in developed countries. Cases often show up first at a primary care practice rather than the emergency room. That’s why front-line documentation matters as much as hospital coding.

Coders who see a Kawasaki diagnosis should also confirm the physician has ruled out other causes of prolonged pediatric fever. Rheumatic fever, coded I00, is one example worth checking before assigning M30.3 to an incomplete presentation.

Key clinical characteristics that appear in supporting documentation include the following. Use digital clinical forms to capture structured symptom documentation at each encounter.

• Fever lasting 5 or more days – the non-negotiable anchor criterion
• Bilateral non-exudative conjunctival injection – red eyes without discharge
• Polymorphous rash – erythematous, variable morphology, often truncal
• Changes in extremities – erythema/edema of palms and soles in acute phase; periungual desquamation in subacute phase
• Oral changes – strawberry tongue, erythema/cracking of lips, diffuse oropharyngeal erythema
• Cervical lymphadenopathy – typically unilateral, node greater than 1.5 cm

The diagnostic criteria that confirm Kawasaki disease

The American Heart Association’s 2017 Kawasaki disease scientific statement, published in Circulation, defines the classic and incomplete diagnostic pathways. Coders should not assign M30.3 unless physician documentation confirms the criteria are met.

Classic Kawasaki disease requires fever lasting 5 or more days plus at least 4 of the 5 principal clinical features listed in the table below. When all 5 features are present, fever may be documented for fewer than 5 days. Physicians experienced with Kawasaki disease can make the diagnosis before day 5 when classic features cluster early.

Incomplete Kawasaki disease applies when fever lasts 5 or more days but fewer than 4 principal features are present. Echocardiography and laboratory findings guide diagnosis in these cases.

Coders should not substitute an alternative code when a physician has documented “incomplete Kawasaki disease” with supporting workup. M30.3 remains the appropriate code when the diagnosis is confirmed, regardless of whether all five features are present.

Other names that still map to ICD-10 code M30.3

Physicians document Kawasaki disease under several interchangeable names. Coders must recognize all of them as mapping to M30.3 to avoid missed or delayed coding.

• Kawasaki disease
• Kawasaki syndrome
• Mucocutaneous lymph node syndrome (MCLS)
• Infantile polyarteritis
• Febrile mucocutaneous lymph node syndrome
• Pediatric systemic vasculitis (when documented as Kawasaki)

When any of these terms appear in the physician’s note alongside a confirmed Kawasaki diagnosis, M30.3 is the correct assignment. If the note reads “rule out Kawasaki disease” or “possible Kawasaki,” code the documented signs and symptoms instead, not M30.3, per ICD-10-CM Official Guidelines for coding uncertain diagnoses in outpatient settings.

Coding guidelines that keep an M30.3 claim clean

Correct use of M30.3 depends on understanding two distinct coding scenarios: the active acute illness and its cardiac sequelae. Errors in either direction create claim denials and audit exposure.

The CMS ICD-10-CM official coding guidelines do not impose an additional-code requirement for Kawasaki disease itself. When coronary artery involvement is documented, though, additional codes capture that complication separately. Practices that build EHR integration into ICD-10 coding workflows cut down on manual lookups and documentation gaps.

• Principal vs. secondary sequencing: When Kawasaki disease is the reason for admission or encounter, code M30.3 as the principal diagnosis. Secondary codes for complications or comorbidities follow.
• Acute vs. sequela coding: For active Kawasaki disease, use M30.3. For long-term coronary artery sequelae documented after the acute phase has resolved, additional or sequela codes may be appropriate depending on the specific complication.
• Uncertain diagnoses (inpatient): When a physician documents “suspected” or “probable” Kawasaki disease in an inpatient setting, code the condition as confirmed per ICD-10-CM Guidelines Section II.H.
• Uncertain diagnoses (outpatient): In outpatient settings, code only confirmed diagnoses. Use symptom codes (fever, rash, lymphadenopathy) for unconfirmed Kawasaki.
• Pediatric vs. adult presentation: M30.3 is not restricted to pediatric patients in the ICD-10-CM tabular, though the condition overwhelmingly affects children. Adult-onset Kawasaki disease, though rare, is coded the same way.
• Excludes1 note: M30.3 excludes microscopic polyarteritis, which is coded M31.7. The two conditions can never appear on the same claim. Beyond this, M30.3 carries no Excludes2, Code First, or Use Additional Code note.

Is M30.3 a billable ICD-10 code?

Yes. ICD-10 code M30.3 is a billable/specific code confirmed across the FY2026 edition of the ICD-10-CM tabular list. It is valid for submission on both the CMS-1500 claim form (used by professional/physician practices) and the UB-04 (used by hospital outpatient and inpatient facilities).

Pabau’s claims management software supports ICD-10-CM code entry and links diagnosis codes to clinical encounter records.

Related ICD-10 codes: Where M30.3 sits inside the M30 category

M30.3 sits within the M30 parent category. Understanding the full M30 sibling set prevents mis-coding when Kawasaki disease is documented alongside, or confused with, other systemic vasculitides. Refer to the AAPC ICD-10-CM code lookup for full tabular navigation alongside these codes.

Do not use M30.2 (Juvenile polyarteritis) when Kawasaki disease is explicitly documented. M30.3 is the specific code for Kawasaki disease. M30.2 refers to a distinct clinical entity.

Coronary artery involvement: How to code the complication correctly

Coronary artery aneurysm is the primary cardiac complication of Kawasaki disease and the reason timely diagnosis and accurate coding matter beyond the acute encounter. When a physician documents coronary artery aneurysm or coronary artery dilation in the context of Kawasaki disease, additional codes capture that specificity.

The sequencing question coders encounter most often: should M30.3 or the cardiac complication code be listed first?

• Acute Kawasaki disease with coronary involvement: M30.3 is the principal diagnosis. Code the coronary artery aneurysm as an additional diagnosis using I25.41, Coronary artery aneurysm. The ICD-10-CM index cross-references I25.41 to aneurysm of the coronary artery due to Kawasaki disease. Q24.5, Malformation of coronary vessels, is the congenital counterpart, and it generally doesn’t apply here, since Kawasaki-related aneurysms are acquired, not congenital.
• Follow-up for coronary sequelae: When the acute illness has resolved and the encounter is specifically for management of coronary artery changes, the coronary code may be the principal diagnosis with a history code for Kawasaki disease.
• Echocardiographic findings only: If echocardiography shows coronary changes and the physician documents them as part of active Kawasaki disease, code M30.3 with additional cardiac codes. Do not code echocardiographic findings alone without physician documentation of the cardiac diagnosis.

The same acquired-versus-congenital logic applies elsewhere in the tabular list. Aortic aneurysm, for example, is reported as I71.9 when it develops after birth, not a congenital code. Verify current payer-specific policies on additional code requirements too, as commercial payers may have local coverage determination nuances for pediatric vasculitis claims.

Accurate ICD-10 coding starts with better documentation tools

Pabau helps pediatric and specialty practices document diagnoses accurately, link ICD-10 codes to clinical records, and streamline claim submission workflows from a single platform.

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How M30.3 groups for DRG and MS-DRG payment

Hospital billing teams need DRG grouping data to anticipate payment and length-of-stay benchmarks. When M30.3 is the principal diagnosis in an inpatient admission, it typically groups to MS-DRG 545, 546, or 547, depending on whether a major or minor complicating condition is also documented.

Consult your facility’s grouper software for the precise FY2026 MS-DRG weight and geometric mean length of stay, since these values change annually with CMS updates. Access the practice management software guide for context on how DRG data integrates into revenue cycle workflows.

Always verify MS-DRG groupings through your facility’s current grouper software. FY2026 weights are set by CMS and may differ from the figures used in the previous fiscal year.

M30.3’s ICD-9 legacy code, for historical claims only

For practices converting historical records or responding to retrospective audits, the ICD-9-CM equivalent of M30.3 is 446.1 (Acute febrile mucocutaneous lymph node syndrome). This is a historical reference only. ICD-9-CM codes have not been valid for new claims submissions since October 1, 2015. Do not submit 446.1 on current claims regardless of the service date.

When responding to payer audits on historical claims from ICD-9 era encounters, use the crosswalk data for context. Document clearly that 446.1 was the correct code for the service date in question.

Documentation habits that keep an M30.3 claim audit-proof

Coding accuracy depends on what the physician documents. These practices protect M30.3 assignments from denial and audit challenge.

• Name the diagnosis explicitly. Notes that describe symptoms without stating “Kawasaki disease” force coders into symptom coding. Physicians should write the confirmed diagnosis by name.
• Document each criterion met. List which of the five clinical features are present. For incomplete Kawasaki, note echocardiography results and laboratory values used to support the diagnosis.
• Record the fever duration. “Fever of 6 days” is sufficient. “Prolonged fever” is not specific enough for confident M30.3 assignment.
• Capture coronary findings separately. If echo shows coronary artery involvement, the note should describe the finding and confirm the physician’s interpretation, not just reference the echocardiogram report.
• Date the acute vs. subacute phase. This supports accurate sequencing when the patient returns for follow-up during desquamation or cardiac surveillance.

Maintaining structured patient records that link diagnosis codes to each encounter note reduces coding lag and supports audit defense. Practices handling pediatric patients also benefit from HIPAA-compliant clinical documentation systems that keep encounter data secure and retrievable.

For teams building out their documentation infrastructure, reviewing clinical documentation workflows can reduce gaps between physician notes and the final coded record. Securing access to sensitive pediatric records matters too, and patient data security tools help practices meet that standard.

Conclusion

Kawasaki disease coding errors usually come from incomplete documentation, not coder unfamiliarity with the code itself. ICD-10 code M30.3 is straightforward. It’s billable, specific, and current through September 30, 2026. The harder part is capturing fever duration, counting the clinical criteria, and coding coronary complications correctly when they show up.

Pabau connects ICD-10 diagnosis codes directly to patient encounter records, cutting down coding lag and supporting cleaner claim submissions for pediatric and specialty practices. To see how that works in practice, book a demo.

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