Table 1.
Summary of the Diagnostic Testing Methods
| Technique | Procedure | Advantages | Disadvantages | Sensitivity, % (Range)221,222 | Specificity, % (Range)221,222 | Turn Around Time | Fungal Viability | Fungal Identity |
|---|---|---|---|---|---|---|---|---|
| KOH and microscopy | - Clean and clip the nail - Scrape the subungual debris onto a glass slide with a #1 curette - Add KOH to dissolve larger keratinocytes - Examine using light microscopy |
- Performed quickly in the office - Inexpensive |
- Low sensitivity - Dependent on physician expertise - Fat droplets, air bubbles, and cotton fibers can interfere with the test |
61 (44–100) | 95 (75–100) | Minutes to hours (depending on nail thickness) | No | No |
| Fungal culture | - Clean and clip the nail - Scrape the subungual debris with a #1 curette onto a paper or cardboard with contrasting background - Grow in laboratory in sabouraud dextrose agar with or without cycloheximide |
High accuracy | - High rate of false negatives - Delay in test results - Contaminants |
56 (29–82) | 99 (83–100) | 3–4 weeks | Yes | Yes |
| Histopathology | - Nail is clipped and placed in 10% buffered formalin - Sample sent to laboratory for hematoxylin and eosin staining (to visualize fungal elements) and periodic acid-Schiff or Grocott methenamine-silver staining (to enhance visualization of the hyphae) |
- Most sensitive technique - Can differentiate from other nail conditions |
Dependent on dermatopathologist expertise | 84 (61–93) | 89 (44–100) | Days | No | No |
| PCR | -Clean and clip the nail -Scrape the subungual debris with a #1 curette onto a paper or cardboard with contrasting background -Send to specialized laboratory, where primers are used to amplify gene fragments |
- Low rate of false negatives | - Expensive - Contaminants |
85–100 | 94–100 | Hours to days | No (Yes, for real-time PCR) | Yes |
Abbreviations: KOH, potassium hydroxide; PCR, polymerase chain reaction.