Laboratories & Physicians
The Sampling Process
Sampling Process
Mycological diagnosis of dermatophyte infections relies on proper sampling strategies and the correct selection of biological material. Several sampling techniques may be used, depending on the clinical presentation, to maximize diagnostic yield for laboratory analysis.
General principles of sampling
The quality of dermatophyte detection is highly dependent on sampling conditions. Whenever possible, specimens should be collected outside the therapeutic window to avoid reduced fungal viability:
- Minimum 15 days after topical antifungal treatment,
- Up to 3 months after systemic antifungal therapy or long-lasting film-forming formulations.
In patients presenting multiple lesions, each anatomical site should be sampled independently to avoid dilution or misrepresentation of fungal burden.
Sampling should target the most active area of infection, corresponding to the interface between affected and clinically healthy tissue, where fungal load is highest.
Depending on lesion type, preferred sampling sites include:
- The active edge of annular or circinate skin lesions
- The zone of nail detachment or subungual debris in onychomycosis
- The peripheral margin of alopecic patches in scalp involvement
Collected material typically includes skin scales, hair shafts, vellus or terminal hairs, nail fragments, and subungual keratinous debris.
For dry, keratinized material, collection into sterile, dry containers is recommended. Dry swabs are not appropriate for routine sampling of dermatophyte infections and should be avoided in this context.
Swab sampling may be considered in selected situations, such as:
- Exudative or suppurative lesions,
- Painful lesions where scraping is limited,
- As a secondary step after curettage, to recover residual surface material.
In such cases, swabs should be moistened with sterile water before use to improve collection efficiency.
Specimens should be placed in sterile, tightly sealed containers and transported under standard conditions. Dermatophytes exhibit prolonged survival in keratinized material such as scales, hair, and nails at room temperature, allowing for reliable transport without specialized preservation requirements.
