ICD-10 Code Q33.3: Agenesis of lung

Key takeaways

ICD-10 Code Q33.3 is a billable ICD-10-CM code for agenesis of lung, the complete congenital absence of one or both lungs.

The code took effect on October 1, 2025 and covers dates of service through September 30, 2026.

Aplasia of lung also indexes to Q33.3, while an underdeveloped lung belongs to Q33.6, so the terms are not interchangeable.

Never put the parent category Q33 on a claim, because only the child codes Q33.0 through Q33.9 are billable.

Unilateral agenesis is survivable and sometimes diagnosed late, so Q33.3 also turns up on adult outpatient claims.

ICD-10 Code Q33.3: Definition and billable status

ICD-10 Code Q33.3 is the billable ICD-10-CM diagnosis code for agenesis of lung, meaning the complete congenital absence of one or both lungs. It took effect on October 1, 2025, and runs through September 30, 2026, under the fiscal year 2026 edition.

Because Q33.3 is a specific code, it goes on a claim as it stands. The Q33 subcategory takes no seventh character and no placeholder X, so nothing else gets added. Injury codes like S25.111D need that extra character, and congenital codes do not.

The code belongs to the American ICD-10-CM edition, which the Centers for Medicare and Medicaid Services (CMS) updates every October. International ICD-10 versions can label the same congenital lung malformations differently. Coders working a retroactive claim should check the edition in force on the date of service.

One distinction causes more trouble here than any other. Agenesis and aplasia of lung both index to Q33.3 in the ICD-10-CM Alphabetic Index. An underdeveloped lung does not, because hypoplasia belongs to Q33.6. The sections below cover the billable facts, the clinical picture, and every sibling code in the Q33 family.

Q33.3 code at a glance

Use the table as a quick lookup before submission, the way you would use a medical coding cheat sheet. It carries every administrative field a payer checks on a Q33.3 claim, plus the two codes most often confused with it.

Agenesis of lung: Clinical overview

Agenesis of lung means the lung never formed. On the affected side there is no lung tissue, no bronchus, and no pulmonary artery.

Lung agenesis is rare, reported at roughly one to two cases per 10,000 live births. Unilateral agenesis is the form that reaches a claim. Bilateral agenesis is not compatible with life.

Which side is missing changes the clinical picture. A systematic review of 137 published cases found the right lung absent in 58% of patients and the left in 42%. Left-sided cases carry the better prognosis, because the mediastinum shifts less and the remaining lung compensates more easily.

Other malformations usually travel with it. In the same review, the associated findings broke down like this:

• Cardiovascular defects in about 40% of patients.
• Skeletal anomalies in about 30%.
• Gastrointestinal malformations in about 20%.
• Genitourinary defects in about 14%.

That pattern shapes the claim. Q33.3 rarely arrives alone, so expect cardiac, skeletal, or gastrointestinal codes on the same encounter, from Q25.8 to Q42.0.

Diagnosis lands at one of two points. Prenatal ultrasound can pick it up when the pulmonary artery on one side is absent and the heart shifts toward the missing lung. That finding often starts life in an OB-GYN record rather than a pediatric one.

After birth, chest radiography was used in 85% of the reviewed cases, with CT in 70% and bronchoscopy in 25%.

Not every case surfaces early. Some patients stay asymptomatic and are only investigated years later for recurrent chest infections. That is why lung agenesis shows up on adult outpatient claims, sitting behind a presenting complaint coded to something like J22.

Three terms describe different stages of the same failure of the lung bud. Boyden separated them in 1955, and ICD-10-CM does not split them the same way.

• Agenesis (Q33.3): no lung tissue, no bronchus, and no pulmonary vessels on the affected side.
• Aplasia (also Q33.3): a short blind-ending bronchus is present, with no lung tissue beyond it. The Alphabetic Index sends aplasia of lung to Q33.3.
• Hypoplasia (Q33.6): the lung is present but underdeveloped. This is a separate billable code, not a variant of Q33.3.

Code from the words in the record. Agenesis needs documented absence of the lung, not a description of a small or underdeveloped one. Query the treating clinician when the note only says the lung is abnormal.

Synonyms and alternate names for Q33.3

These terms all map to ICD-10 Code Q33.3 when the record supports absence of lung tissue. Coders meet them in radiology reports, discharge summaries, and operative notes.

• Pulmonary agenesis
• Congenital absence of lung
• Absent lung, congenital
• Aplasia of lung, unilateral or bilateral
• Unilateral pulmonary agenesis, meaning one lung is absent
• Bilateral pulmonary agenesis, meaning both lungs are absent

Look up “agenesis” in the ICD-10-CM Alphabetic Index and the entry for lung points to Q33.3. Confirm it in the Tabular List before you code. The same index-then-tabular order applies across the Q30 to Q34 block, Q30.8 included.

Parent category: Q33 congenital malformations of lung

Q33 is the non-billable parent category for congenital malformations of lung. It groups the child codes for administrative purposes and cannot go on a claim. Every submission needs one of the child codes, Q33.0 through Q33.9, and Q33.3 is one of them.

Where Q33.3 sits in the ICD-10-CM hierarchy

The path runs from the chapter down to the billable code:

• ICD-10-CM
• Q00 to QA0: congenital malformations, deformations, and chromosomal abnormalities
• Q30 to Q34: congenital malformations of the respiratory system
• Q33: congenital malformations of lung, the non-billable parent
• Q33.3: agenesis of lung, billable

This matters at the payer edit stage. A claim carrying the category code Q33 gets rejected, because the payer expects a specific child code. The same category-versus-child rule runs through every chapter, injury codes like S23.110A included.

Sibling codes: Other congenital lung malformations under Q33

The Q33 family holds nine billable child codes, and picking the wrong one is a common error on congenital lung claims. The table lists every descriptor, its billable status, and what the record has to show. Excludes1 notes are included, since they decide whether a code survives a payer edit.

Sequestration is the sibling most often swapped for agenesis, so it is worth a closer look.

Q33.3 vs Q33.2: Agenesis vs sequestration of lung

Sequestration means lung tissue is present but disconnected, while agenesis means there is no lung at all. Both involve abnormal development, so the documentation clues decide the code.

So the report decides it. A mass with systemic arterial supply is Q33.2, and an absent lung is Q33.3.

Coding guidelines and usage notes for ICD-10 Code Q33.3

Q33.3 carries no code-first note, no use-additional-code note, and no Excludes1 or Excludes2 note at code level in the FY2026 edition. That leaves the documentation language as the only thing standing between the diagnosis and the right code.

• Assign Q33.3 only for documented absence of lung tissue. “Small lung” or “underdeveloped lung” points to Q33.6 instead.
• Treat aplasia of lung as Q33.3. A rudimentary blind-ending bronchus with no lung beyond it still indexes to this code.
• Never submit the parent code Q33. It is a category header for grouping, and it fails claim edits.
• No laterality character exists. Q33.3 covers unilateral and bilateral agenesis, so the side belongs in the clinical note.
• Sequence by the circumstances of the encounter. Q33.3 has no sequencing rule of its own, so the general ICD-10-CM rules for principal and secondary diagnoses apply.
• Query before you guess. The CDC ICD-10-CM browser confirms the descriptor for a given fiscal year, but only the clinician can confirm the anatomy.

Capturing the clinician’s own words at the point of care removes most retrospective queries. Digital intake forms and clinical documentation software keep that language in the record, where a coder can find it.

The riskiest records are the ones that say only “abnormal lung” without naming absence, size, or bronchial connection. Those three details separate Q33.3, Q33.6, and Q33.2.

When is ICD-10 Code Q33.3 used for reimbursement?

Q33.3 is used whenever a documented absence of lung shapes the care being billed. In practice that means a short list of encounter types.

• Neonatal and pediatric inpatient claims: the diagnosis is established on imaging soon after birth, sometimes alongside a newborn respiratory code such as P22.0. Q33.3 takes the principal position when agenesis drove the admission.
• Outpatient specialist visits: pulmonologists and cardiothoracic surgeons code Q33.3 as a chronic background diagnosis alongside the presenting problem.
• Surgical encounters: procedures addressing the consequences, such as scoliosis correction or cardiac repair, carry Q33.3 as an additional diagnosis for context.
• Late diagnostic workups: adults investigated for recurrent chest infections sometimes turn out to have one lung, and Q33.3 explains the imaging.
• Documentation payers expect: a CT or MRI report confirming absent lung tissue, an operative note, or a physician attestation naming pulmonary agenesis.

Payers request supporting records on rare congenital codes more often than on everyday diagnoses. Keeping imaging reports and attestations attached to the patient’s clinical record shortens that exchange.

Practices running pulmonary rehabilitation programs field the same requests, and Pabau’s physical therapy software keeps those notes on one record.

Effective date and code validity for Q33.3

Q33.3 took effect on October 1, 2025 and stays valid through September 30, 2026. The annual ICD-10-CM update cycle is published by the CDC and the National Center for Health Statistics. The FY2027 files will confirm whether anything about the code changes.

Q33.3 has been stable across recent editions, with no descriptor change in the FY2026 update. For a date of service before October 1, 2025, code from the FY2025 edition instead. The same year-by-year check applies to every other code on the claim.

How Pabau supports accurate Q33.3 coding and claim documentation

In many practices the coder works one system away from the evidence. The imaging report sits in one place, the clinician’s note in another, and the claim in a third. Queries then go out by email and come back days later, if they come back at all.

Pabau keeps the patient record, the clinical note, the intake forms, and the invoice on one timeline. A coder checking a Q33.3 assignment can read the wording the clinician chose. The supporting imaging report then attaches to the claim from inside the same record.

The result is fewer retrospective queries and a faster answer when a payer asks for proof. Every subscription includes the full platform, so records, forms, and billing work together from the first week.

Keep coding decisions tied to the clinical record

Pabau brings patient records, clinical notes, intake forms, and billing into one system. Coders can see the documentation behind every diagnosis code, so rare codes like Q33.3 are easier to support when a payer asks.

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Conclusion

Q33.3 is a small code with a narrow trigger. Use it when the record says a lung is absent. Move to Q33.6 the moment the record says the lung is present but underdeveloped.

Check the Alphabetic Index entry even when the descriptor already feels familiar. Aplasia of lung lands on Q33.3, which trips up experienced coders. Hypoplasia lands outside it, which trips up everyone else.

Congenital claims also arrive with company, so expect cardiac, skeletal, or gastrointestinal codes on the same encounter. Book a demo to see how Pabau keeps diagnosis coding, clinical notes, and claims in one place for your practice.

Continue your research

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