Onychomycosis, also known as tinea unguium, is a common fungal infection that affects the nails, causing thickening, discoloration, and brittleness. Accurate diagnosis and coding are crucial not only for effective treatment but also for proper reimbursement in medical billing. With the 2025 ICD-10-CM updates, medical professionals need to ensure they’re using the correct codes for onychomycosis and related fungal conditions.
This guide categorizes the ICD-10 codes by affected body regions—feet, hands, and other related conditions—making it easier for practitioners to identify the right code for every scenario.
What is Onychomycosis and How Does ICD-10 Help in Accurate Diagnoses?
Onychomycosis, also known as tinea unguium, is a fungal infection that primarily affects the nails, leading to discoloration, thickening, and brittleness. It is caused by dermatophytes, yeasts, or molds and is more prevalent in toenails than fingernails. This condition can cause discomfort, impact nail function, and, if untreated, lead to secondary infections.
ICD-10 Code for Onychomycosis
The most relevant ICD-10 code for onychomycosis is B35.1, which covers dermatophytic onychia, dermatophytosis of nails, and ringworm of nails. This code is crucial for documenting fungal infections accurately in medical records.
Role of ICD-10 in Diagnosing Onychomycosis
- Standardizes diagnosis for reimbursement purposes.
- Ensures clarity in medical documentation.
- Aids in differentiating nail and skin infections.
- Provides global consistency in diagnosis coding.
- Facilitates tracking of treatment and outcomes.
ICD-10 coding not only helps in accurate diagnosis but also streamlines the treatment process by enabling precise communication between healthcare providers and insurers. This ensures patients receive timely and effective care.
Breaking Down Onychomycosis ICD-10 Codes by Body Region
Onychomycosis, also called tinea unguium, is a fungal infection of the nails caused by dermatophytes, yeasts, or molds. Accurate ICD-10 coding ensures proper documentation for diagnosis and reimbursement. The primary code for onychomycosis is B35.1, which became effective in the 2025 ICD-10-CM update.
Below is a detailed breakdown of onychomycosis and related fungal infection codes by affected body regions, addressing key keywords and scenarios.
1. Onychomycosis of Feet (Toenails)
Fungal infections in toenails are the most common form of onychomycosis, often caused by dermatophytes. These infections may also affect the skin of the feet.
- B35.1: Onychomycosis due to dermatophyte, applicable to fungal nails, toenail fungus, and nail discoloration.
Example: ICD-10 code for onychomycosis both feet.
- B35.3: Tinea pedis (athlete’s foot) includes foot fungus infections.
Example: ICD-10 code for athletes’ foot.
- L03.03: Cellulitis of toe caused by fungal infections, a common secondary complication
Example: Thick toenails ICD-10.
2. Onychomycosis of Hands (Fingernails)
Fingernail infections are less common but require distinct coding for precise diagnosis.
- B35.1: Onychomycosis caused by dermatophytes, used for fingernail fungus and brittle nails.
Example: Fingernail fungus ICD-10.
- B35.2: Tinea manuum, a fungal infection affecting the skin of the hands, often seen with nail infections.
Example: ICD-10 code for fungal infections of the hand.
- L03.01: Cellulitis of the finger caused by fungal infections, associated with severe cases.
3. Skin Fungal Infections Related to Onychomycosis
Skin infections often accompany nail infections, requiring additional ICD-10 codes to document broader conditions.
- B35.9: Dermatophytosis, unspecified, applicable when the specific infection site is not documented.
Example: Ringworm ICD-10.
- B35.4: Tinea corporis, or ringworm of the body, often associated with nail fungal infections.
Example: ICD-10 tinea corporis.
- B35.6: Tinea cruris (jock itch), a fungal infection of the groin.
Example: Jock itch ICD-10.
- B36.9: Superficial mycosis, unspecified, used for fungal infections without defined locations.
4. Scalp and Other Specific Fungal Infections
Scalp or hair-related fungal infections are often seen in patients with broader dermatophyte issues.
- B35.0: Tinea capitis (scalp ringworm), primarily affects the scalp and hair.
Example: ICD-10 code for tinea capitis.
- B36.0: Tinea versicolor, a yeast infection causing skin pigmentation changes.
Example: ICD-10 code for tinea versicolor.
5. Comorbid Conditions and Multiple Nail Infections
When fungal infections coexist with other conditions, specific ICD-10 codes must be used.
- B35.1: Onychomycosis of multiple toenails with type 2 diabetes mellitus.
Example: Onychomycosis of multiple toenails with type 2 diabetes mellitus ICD-10.
Additional ICD-10 Codes for Fungal Infections and Related Conditions
1. Nail Disorders Associated with Fungal Infections
These codes address nail-specific abnormalities often caused or worsened by fungal infections.
- L60.0 – Ingrowing nail: Used when fungal infections cause nail deformities leading to pain or embedded growth.
- L60.2 – Onychogryphosis: Thickened, claw-like nails resulting from untreated or chronic fungal infections.
- L60.3 – Nail dystrophy: Applies to structural abnormalities of the nail caused by fungal infections like onychomycosis.
2. Skin and Soft Tissue Complications of Fungal Infections
Secondary infections and related skin conditions frequently result from untreated fungal infections.
- L03.115 – Cellulitis of the right lower limb: Used for fungal infections causing severe inflammation in the right foot.
3. Systemic Conditions Linked to Fungal Infections
These codes address comorbidities, such as diabetes, that may exacerbate fungal infections.
- E11.620 – Type 2 diabetes mellitus with diabetic dermatitis: Used for patients with diabetes and fungal skin or nail infections.
- L62 – Nail disorders in diseases classified elsewhere: Covers nail complications arising from systemic conditions like diabetes.
4. General or Unspecified Fungal Infections
For fungal infections with unspecified types or locations, these codes offer broader documentation options.
- B49 – Unspecified mycosis: Covers fungal infections where the specific site or type is not documented.
- B36.1 – Tinea nigra: Pigmented fungal patches that may accompany nail infections in rare cases.
5. History and Skin Changes Related to Fungal Infections
These codes document prior fungal infections and related changes in skin or nail conditions.
- Z86.31 – Personal history of (healed) mycoses: For documenting susceptibility due to previous fungal infections.
- R23.8 – Other skin changes: Used for conditions like nail discoloration or thickened skin caused by fungal infections.
How Accurate ICD-10 Coding Supports Reimbursement for Fungal Infections
Accurate ICD-10 coding is vital for securing proper reimbursement for fungal infections like onychomycosis. Codes such as B35.1 ensure precise documentation, improving communication with insurers and reducing claim denials. This level of accuracy streamlines billing processes, ensuring faster and more efficient payments.
Outsourcing to a professional infectious disease billing service helps healthcare providers ensure accurate coding for fungal infections, including cases with comorbidities like diabetes. These services specialize in maximizing reimbursements, maintaining compliance, and reducing administrative burdens for medical practices.
Closing Remarks
Accurate ICD-10 coding is essential for the proper diagnosis, treatment, and reimbursement of fungal infections like onychomycosis. Using specific codes like B35.1 ensures precise documentation, minimizes claim denials, and enhances communication with insurers. This level of accuracy supports smoother billing processes and better financial outcomes.
By prioritizing accurate coding practices, healthcare providers can maximize reimbursements while maintaining compliance with industry regulations. Proper ICD-10 coding not only simplifies medical billing but also allows providers to focus on delivering high-quality care to their patients.
