B27.99 Infectious mononucleosis, unspecified with other complication

The ICD-10-CM code for Infectious mononucleosis, unspecified with other complication is B27.99 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

1: Certain infectious and parasitic diseases (A00-B99)

Section

B25-B34: Other viral diseases (B25-B34)

Category B27

21 codes (16 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to B27.99:

• Mononucleosis, infectious › with › complication NEC

Inclusion Terms

• Hepatomegaly in unspecified infectious mononucleosis

U.S. Hospital Utilization

• An estimated 400 U.S. inpatient stays in 2023 included B27.99 among the documented diagnoses.
• 235 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

HIV Infections (TOC entry)

a. Human Immunodeficiency Virus (HIV) Infections .............................................................. 19

Infectious agents causing diseases in other chapters (TOC)

b. Infectious agents as the cause of diseases classified to other chapters ................................. 22

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)