A37.91 ICD-10-CM Code: Whooping cough, unspecified species with pneumonia
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Other bacterial diseases (A30-A49)
A37.91
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceWhooping cough, unspecified species with pneumonia
Whooping cough (pertussis) caused by an unspecified bacterial species that has developed into pneumonia (lung infection). This is a serious respiratory infection where the patient has both the characteristic severe cough of whooping cough and inflammation of the lungs.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
N/A—
Not mapped
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for A37.91 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A37.91 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for A37.91 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for A37.91 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A37.91 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for A37.91 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for A37.91 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is A37.91 an HCC code?
No. A37.91 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A37.91 is the ICD-10-CM diagnosis code for whooping cough, unspecified species with pneumonia. Whooping cough (pertussis) caused by an unspecified bacterial species that has developed into pneumonia (lung infection). This is a serious respiratory infection where the patient has both the characteristic severe cough of whooping cough and inflammation of the lungs. A37.91 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other bacterial diseases (a30-a49).
A37.91 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Use this code only when the causative organism of pertussis is not specified or documented; if the organism is identified (Bordetella pertussis, parapertussis, or bronchiseptica), use the more specific A37.0x, A37.1x, or A37.8x codes instead.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A37.91 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the causative organism of pertussis is not specified or documented; if the organism is identified (Bordetella pertussis, parapertussis, or bronchiseptica), use the more specific A37.0x, A37.1x, or A37.8x codes instead
- •The pneumonia component is included in this code, so do not assign a separate pneumonia code; ensure documentation supports both whooping cough and pneumonia before coding