What is the ICD10 (International Classification of Diseases, 10th Revision) code for a right toenail infection?

ICD-10 Code for Right Toenail Infection

The appropriate ICD-10 code depends on the specific type of toenail infection: for fungal infection (onychomycosis), use B35.1; for bacterial infection with cellulitis, use L03.116; for acute paronychia, use L03.011 (right finger) or L03.041 (right toe); and for chronic paronychia, use L03.031.

Coding Algorithm Based on Clinical Presentation

Fungal Toenail Infection (Onychomycosis)

• B35.1 - Tinea unguium (dermatophytic onychomycosis of toenails) 1

  • This is the most common toenail infection, with toenails affected in 80% of all onychomycosis cases 1
  • Distal and lateral subungual onychomycosis (DLSO) is the most frequent presentation, where the fungus invades the nail and nail bed by penetrating the distal or lateral margins 1
  • The affected nail becomes thickened and discolored with varying degrees of onycholysis 1

• B37.2 - Candidal onychomycosis (if yeast infection confirmed) 1

  • Less common than dermatophyte infection, accounting for 5-10% of onychomycosis cases 1
  • Toenails are less commonly affected than fingernails in Candida infections 1

Bacterial Toenail Infections

• L03.116 - Cellulitis of right toe 1

  • Use when there is bacterial soft tissue infection with signs of inflammation: erythema, warmth, pain/tenderness, induration, or purulent discharge 1
  • Particularly important in diabetic patients where infected wounds can lead to serious complications 1

• L03.011 - Cellulitis of right finger (if documenting paronychia affecting nail fold)

• L03.041 - Acute paronychia of right toe

• L03.031 - Chronic paronychia of right toe 1

Key Clinical Distinctions for Accurate Coding

Fungal vs. Bacterial Differentiation

• Fungal infections typically present with gradual onset, nail thickening, discoloration (white, yellow, or brown), and subungual hyperkeratosis without acute inflammation 1
• Bacterial infections present with acute inflammation signs: erythema >0.5 cm around the wound, local warmth, tenderness, swelling, and potentially purulent discharge 1

Laterality Specification

• ICD-10-CM provides improved specificity over ICD-9-CM by capturing laterality (right vs. left) 2
• Always specify "right" in the code when the right toenail is affected to ensure accurate tracking and reimbursement 2

Common Coding Pitfalls to Avoid

• Do not code based on clinical appearance alone - Fungal infections require mycological confirmation through positive culture, direct microscopy, or histological examination before definitive coding 1
• Avoid using soft tissue culture results for coding osteomyelitis if bone involvement is suspected, as they do not accurately reflect bone pathology 1
• Do not confuse chronic paronychia with onychomycosis - Chronic paronychia (L03.031) involves nail fold inflammation, while onychomycosis (B35.1) is nail plate infection 1
• Ensure encounter type is specified - The code should indicate initial encounter for active treatment when applicable 3

Documentation Requirements

• Document specific clinical findings: nail thickening, discoloration pattern, presence of onycholysis, involvement of nail bed vs. nail plate 1
• Record any confirmatory testing: KOH preparation, fungal culture, or bacterial culture results 1
• Note extent of involvement: number of affected toenails, percentage of nail plate affected, presence of matrix involvement 1
• In diabetic patients, document presence of any systemic signs (fever, elevated WBC, tachycardia) that would indicate severity 1