2027 ICD-10-CM Diagnosis Code Q42.9Congenital absence, atresia and stenosis of large intestine, part unspecified

ICD-10-CM Codes›Q00-Q99›Q38-Q45›Q42

ICD-10-CM Q42.9
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q42.9 is a billable ICD-10-CM diagnosis code for congenital absence, atresia and stenosis of large intestine, part unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 393 through 395. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 8 closely related codes. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Digestive congenital anomalies.

For Medicare Advantage risk adjustment, Q42.9 maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation) under the V28 model, adding a risk factor of about 0.326 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
Q42.9
Billable Status
Yes — Valid for Submission
Code Describes
Congenital absence, atresia and stenosis of large intestine, part unspecified
Short Description
Congen absence, atresia and stenosis of lg int, part unsp
Parent Code
Q42
Congenital absence, atresia and stenosis of large intestine

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ38-Q45Other congenital malformations of the digestive system
CategoryQ42Congenital absence, atresia and stenosis of large intestine
This CodeQ42.9Congenital absence, atresia and stenosis of large intestine, part unspecified

Present on Admission (POA)Billing

Q42.9 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Other congenital malformations of the digestive system (Q38-Q45).

Medicare Risk Adjustment (HCC)Billing

Q42.9 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 78— Intestinal Obstruction/Perforation
Payment HCC · PY 2027 one of 76 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.326
community, non-dual, aged · ranges 0.326–0.688 across segments
Hierarchy
Superseded by HCC 77
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
Not mapped
Q42.9 does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Aplasia of colon
  • Atresia and stenosis of large intestine, rectum and anal canal
  • Congenital absence of large intestine
  • Congenital atresia of colon
  • Congenital atresia of large intestine
  • Congenital hypoplasia of colon
  • Congenital hypoplasia of intestinal tract
  • Congenital obstruction of large intestine
  • Congenital stenosis of colon
  • Congenital stenosis of large intestine
  • Imperforate large intestine
  • Stenosis of colon

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q42.9: its own notes plus those printed at Q42 and Chapter 17. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Q42 Congenital absence, atresia and stenosis of large intestine applies to 6 codes
  • congenital obstruction, occlusion and stricture of large intestine

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • inborn errors of metabolism (E70-E88)

Notes

General instructions on how these codes are used.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • Codes from this chapter are not for use on maternal records

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Q42.9, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming Q42.9: they are not reported together with it, unless the two conditions are unrelated.

  • K56 Paralytic ileus and intestinal obstruction without hernia
    congenital stricture or stenosis of intestine (Q41-Q42) names Q41-Q42, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MAL002
Digestive congenital anomalies
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Birth Defects

A birth defect is a problem that happens while a baby is developing in the mother's body. Most birth defects happen during the first 3 months of pregnancy. One out of every 33 babies in the United States is born with a birth defect.

The full article covers:

  • What are birth defects?
  • What causes birth defects?
  • Who is at risk of having a baby with birth defects?
  • How are birth defects diagnosed?
  • What are the treatments for birth defects?
  • Can birth defects be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Q42.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
751.2 Atresia large intestine
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Q42.9Overview

Is Q42.9 (Congenital absence, atresia and stenosis of large intestine) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report congenital absence, atresia and stenosis of large intestine, part unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does Q42.9 group to?

When congenital absence, atresia and stenosis of large intestine, part unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 394, 395, 393, with relative weights from 0.6379 to 1.5877 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q42.9 a CC or MCC?

CMS lists Q42.9 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 8 closely related codes in its exclusion list.

Is Q42.9 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for congenital absence, atresia and stenosis of large intestine, part unspecified on inpatient claims. The code appears in the Other congenital malformations of the digestive system (Q38-Q45) range of the CMS exempt list.

What is the ICD-9 equivalent of Q42.9?

Under the General Equivalence Mappings, congenital absence, atresia and stenosis of large intestine, part unspecified converts to ICD-9-CM 751.2 (atresia large intestine). The mapping is approximate, so confirm the match fits the documentation.

What HCC is Q42.9?

Q42.9 (congenital absence, atresia and stenosis of large intestine, part unspecified) maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation), commonly written as HCC 78, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It does not map to any RxHCC in the Part D prescription drug model.

Does Q42.9 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, Q42.9 adds a risk adjustment factor of about 0.326 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.326 to 0.688 depending on the payment segment). A more severe related category (HCC 77) supersedes it when both are reported. See the full factor table on the HCC 78 category page.