2026 ICD-10-CM Diagnosis Code A37.91Whooping cough, unspecified species with pneumonia
ICD-10-CM Codes›A00–B99›A30-A49›A37
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Not Chronic
A37.91 is a billable ICD-10-CM diagnosis code for whooping cough, unspecified species with pneumonia. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 202 through 203. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 133 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Bacterial infections and Pneumonia (except that caused by tuberculosis).
Code Identity
Code Classification
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
with pneumonia A37.91
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Pneumonia
Pneumonia is an infection in one or both of your lungs. It causes the air sacs of your lungs to fill up with fluid or pus. Pneumonia can range from mild to severe, depending on what caused it, your age, and your overall health.
The full article covers:
- What is pneumonia?
- What causes pneumonia?
- Who is more likely to develop pneumonia?
- What are the symptoms of pneumonia?
- What other problems can pneumonia cause?
- How is pneumonia diagnosed?
- What are the treatments for pneumonia?
- Can pneumonia be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert A37.91 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About A37.91Overview
What is the ICD-10 code for whooping cough, unspecified species with pneumonia?
The ICD-10-CM code for whooping cough, unspecified species with pneumonia is A37.91 (sometimes written as A3791). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is A37.91 (Whooping cough, unspecified species) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report whooping cough, unspecified species with pneumonia on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does A37.91 group to?
When whooping cough, unspecified species with pneumonia is the principal diagnosis on an inpatient stay, it groups to MS-DRG 202, 203, with relative weights from 0.6700 to 0.9712 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A37.91 a CC or MCC?
CMS lists A37.91 as an MCC (major complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 133 closely related codes in its exclusion list.
What is the ICD-9 equivalent of A37.91?
Under the General Equivalence Mappings, whooping cough, unspecified species with pneumonia converts to ICD-9-CM 033.9 (whooping cough NOS) and 484.3 (pneumonia in whoop cough). The mapping is approximate, so confirm the match fits the documentation.
