2024 ICD-10-CM Diagnosis Code B27.9

Infectious mononucleosis, unspecified

ICD-10-CM Code:
B27.9
ICD-10 Code for:
Infectious mononucleosis, unspecified
Is Billable?
Not Valid for Submission
Code Navigator:

Code Classification

  • Certain infectious and parasitic diseases
    (A00–B99)
    • Other viral diseases
      (B25-B34)
      • Infectious mononucleosis
        (B27)

B27.9 is a non-specific and non-billable diagnosis code code, consider using a code with a higher level of specificity for a diagnosis of infectious mononucleosis, unspecified. The code is not specific and is NOT valid for the year 2024 for the submission of HIPAA-covered transactions. Category or Header define the heading of a category of codes that may be further subdivided by the use of 4th, 5th, 6th or 7th characters.

Unspecified diagnosis codes like B27.9 are acceptable when clinical information is unknown or not available about a particular condition. Although a more specific code is preferable, unspecified codes should be used when such codes most accurately reflect what is known about a patient's condition. Specific diagnosis codes should not be used if not supported by the patient's medical record.

Specific Coding Applicable to Infectious mononucleosis, unspecified

Non-specific codes like B27.9 require more digits to indicate the appropriate level of specificity. Consider using any of the following ICD-10-CM codes with a higher level of specificity when coding for infectious mononucleosis, unspecified:

  • Use B27.90 for Infectious mononucleosis, unspecified without complication - BILLABLE CODE

  • Use B27.91 for Infectious mononucleosis, unspecified with polyneuropathy - BILLABLE CODE

  • Use B27.92 for Infectious mononucleosis, unspecified with meningitis - BILLABLE CODE

  • Use B27.99 for Infectious mononucleosis, unspecified with other complication - BILLABLE CODE

Clinical Information

  • Fatigue Syndrome, Chronic

    a syndrome characterized by persistent or recurrent fatigue, diffuse musculoskeletal pain, sleep disturbances, and subjective cognitive impairment of 6 months duration or longer. symptoms are not caused by ongoing exertion; are not relieved by rest; and result in a substantial reduction of previous levels of occupational, educational, social, or personal activities. minor alterations of immune, neuroendocrine, and autonomic function may be associated with this syndrome. there is also considerable overlap between this condition and fibromyalgia. (from semin neurol 1998;18(2):237-42; ann intern med 1994 dec 15;121(12): 953-9)
  • Herpesvirus 4, Human

    the type species of lymphocryptovirus, subfamily gammaherpesvirinae, infecting b-cells in humans. it is thought to be the causative agent of infectious mononucleosis and is strongly associated with oral hairy leukoplakia (leukoplakia, hairy;), burkitt lymphoma; and other malignancies.
  • Infectious Mononucleosis

    a common, acute infection usually caused by the epstein-barr virus (herpesvirus 4, human). there is an increase in mononuclear white blood cells and other atypical lymphocytes, generalized lymphadenopathy, splenomegaly, and occasionally hepatomegaly with hepatitis.
  • Fibromyalgia

    a common nonarticular rheumatic syndrome characterized by myalgia and multiple points of focal muscle tenderness to palpation (trigger points). muscle pain is typically aggravated by inactivity or exposure to cold. this condition is often associated with general symptoms, such as sleep disturbances, fatigue, stiffness, headaches, and occasionally depression. there is significant overlap between fibromyalgia and the chronic fatigue syndrome (fatigue syndrome, chronic). fibromyalgia may arise as a primary or secondary disease process. it is most frequent in females aged 20 to 50 years. (from adams et al., principles of neurology, 6th ed, p1494-95)

Patient Education


Infectious Mononucleosis

Infectious mononucleosis, or "mono", is an infection usually caused by the Epstein-Barr virus. The virus spreads through saliva, which is why it's sometimes called "kissing disease." Mono occurs most often in teens and young adults. However, you can get it at any age. Symptoms of mono include:

  • Fever
  • Sore throat
  • Swollen lymph glands

Sometimes you may also have a swollen spleen. Serious problems are rare.

A blood test can show if you have mono. Most people get better in two to four weeks. However, you may feel tired for a few months afterward. Treatment focuses on helping symptoms and includes medicines for pain and fever, warm salt water gargles and plenty of rest and fluids.


[Learn More in MedlinePlus]

Code History

  • FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
  • FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
  • FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.