ICD-11 Codes
for 4A00.0 - Functional neutrophil defects

Teodor Jurukovski January 1, 1970

Fact checked by: Teodor Jurukovski

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Understanding functional neutrophil defects

Functional neutrophil defects are a group of primary immunodeficiency disorders arising from abnormalities in innate immunity. They are classified in ICD-11 under code 4A00.0. In these conditions, neutrophils are present in normal or near normal numbers but are unable to perform essential immune functions effectively.

Neutrophils are a critical component of the first line of defense against infection. They migrate to sites of infection, adhere to blood vessel walls, ingest invading microorganisms, and destroy them using antimicrobial enzymes and reactive oxygen species. When any of these processes are impaired, susceptibility to infection increases significantly.

Individuals with functional neutrophil defects commonly experience recurrent, severe, and sometimes life threatening bacterial and fungal infections, often beginning in infancy or early childhood.

Alternative names for functional neutrophil defects

Several alternative terms are used in clinical practice and historical literature to describe functional neutrophil defects. Awareness of these synonyms is important for accurate documentation and case identification.

ICD-11 also provides additional specificity through 4A00.0Y for other specified functional neutrophil defects and 4A00.0Z for functional neutrophil defects, unspecified.

Origins and pathophysiology

Functional neutrophil defects are most commonly caused by inherited genetic mutations that disrupt normal neutrophil development or activity. These mutations interfere with critical immune processes required for effective microbial clearance.

Impaired mechanisms may include defective chemotaxis, reduced adherence to vascular endothelium, abnormal phagocytosis, or failure of the oxidative burst needed to kill pathogens. As a result, infections persist despite adequate neutrophil numbers.

Several well characterised genetic disorders fall within this category, including leukocyte adhesion deficiencies, Chediak-Higashi syndrome, chronic granulomatous disease, and Wiskott-Aldrich syndrome.

Recognising clinical features

The hallmark of functional neutrophil defects is recurrent, severe, and often unusual infections. These infections are most commonly bacterial or fungal and may be resistant to standard therapies.

In certain conditions, delayed separation of the umbilical cord may be an early clinical clue to an underlying neutrophil adhesion defect.

Diagnosis of functional neutrophil defects

Diagnosis requires a comprehensive immunological assessment aimed at identifying defects in neutrophil function rather than quantity. Evaluation typically begins with basic immune profiling and progresses to specialised functional testing.

Genetic testing plays a central role in confirming inherited forms and guiding prognosis, family counselling, and treatment decisions. The ICD-11 code 4A00.0Z is used when the specific defect has not yet been fully characterised.

Management and treatment strategies

Management focuses on preventing infections, treating them promptly, and addressing the underlying immune dysfunction where possible. Treatment plans are individualised based on the specific defect and disease severity.

Long term care requires a multidisciplinary approach involving immunology, hematology, and infectious disease specialists to monitor complications and optimise outcomes.

Are functional neutrophil defect ICD codes billable

Yes. ICD-11 code 4A00.0 and its related subcodes are billable when supported by appropriate clinical evaluation and diagnostic testing. Accurate documentation of infection history, laboratory findings, and genetic confirmation is essential to support correct coding and reimbursement.