Can a sample be taken for a suspected fungal infection of the nail if the patient is wearing nail polish?

Nail Polish Must Be Removed Before Taking a Sample for Suspected Fungal Nail Infection

Nail polish should be completely removed before taking a sample for suspected fungal nail infection, as it can interfere with proper diagnosis and lead to false negative results. 1, 2

Why Nail Polish Interferes with Fungal Testing

• Nail polish creates a physical barrier that prevents access to the infected nail material
• It can interfere with microscopic examination by obscuring fungal elements
• Chemical components in nail polish may inhibit fungal growth in culture
• Accurate diagnosis is critical as 50% of nail dystrophies are non-fungal in origin 1, 2

Proper Sampling Technique for Suspected Onychomycosis

1. Remove all nail polish completely before attempting to collect a sample

2. Identify the most appropriate area for sampling:

   • For distal lateral subungual onychomycosis (DLSO): Collect subungual debris from the most proximal part of the infection
   • For superficial white onychomycosis (SWO): Scrape the surface of the infected nail plate
   • For proximal subungual onychomycosis (PSO): Scrape with a scalpel blade 1

3. Use appropriate collection tools:

   • Small dental scraper for obtaining material beneath the nail
   • Scalpel blade for surface scraping
   • Consider cutting back onycholytic nail and scraping the underside 1

4. Collect as much material as possible due to the paucity of fungal elements 1, 2

Laboratory Testing Process

After proper sample collection (without nail polish):

1. Direct microscopy: Place sample on glass slide with 20% potassium hydroxide for 15-20 minutes

   • Addition of Parker's blue/black ink may enhance visualization of hyphae
   • Calcofluor white staining can improve visualization 1

2. Culture: Remaining material should be cultured on Sabouraud's glucose agar with antibiotics

   • Incubate at 28°C for at least 3 weeks before declaring negative 1

3. Advanced testing (if needed):

   • Histopathology with periodic acid–Schiff staining (more sensitive than direct microscopy/culture)
   • Molecular diagnostic techniques like PCR for faster results 1, 2

Importance of Accurate Diagnosis

• The American Academy of Dermatology explicitly states: "Do not prescribe oral antifungal therapy for suspected nail fungus without confirmation of fungal infection" 1
• The most common cause of treatment failure in the UK is incorrect diagnosis made on clinical grounds alone 1
• Treatment is lengthy and expensive, making accurate diagnosis crucial 1, 3
• 70% of GPs would only treat a suspected nail infection with oral antifungals after laboratory confirmation 3

Clinical Implications

• Onychomycosis should not be considered a trivial disease as it can lead to complications like cellulitis in elderly or diabetic patients 1, 2
• Misdiagnosis and inappropriate treatment can lead to unnecessary drug exposure, side effects, and costs 1
• Treatment duration is substantial (6 months for fingernails, 12 months for toenails), making accurate diagnosis essential 1, 2

Remember that nail polish must be completely removed to ensure proper sample collection and accurate diagnosis of fungal nail infections. This simple step is critical for avoiding misdiagnosis and ensuring appropriate treatment.