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Textbook/Dermatology/Skin scraping, microscopy and culture
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Skin scraping, microscopy and culture

Select and collect high-yield skin, hair and nail specimens for microscopy and culture, interpret negative results cautiously, and protect patient and staff safety.

22 min full readUK scopeSources checked 27 Aug 2026Clinical review pending
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Time-critical presentation

Escalate urgently when assessment for Skin scraping, microscopy and culture reveals systemic toxicity, airway or eye involvement, extensive skin failure, a non-blanching eruption in an unwell patient, or a rapidly changing lesion suspicious for aggressive malignancy.

Open the sections you need. The overview is shown first.
01Purpose and principlesWhat the assessment is for and the core concepts behind it.

Sampling error is the commonest avoidable limitation. For annular skin disease, scrape the advancing scaly edge rather than the cleared centre. In onychomycosis, remove superficial debris and collect subungual material or diseased nail as proximally as safely possible. For tinea capitis, submit plucked abnormal hairs, brushings or scrapings according to laboratory instructions.

Potassium hydroxide microscopy detects hyphae or spores but depends on specimen quality and reader experience. Culture can identify an organism and inform epidemiology or difficult treatment, yet contamination and slow growth complicate interpretation. Repeat sampling or consider an alternative diagnosis when clinical and laboratory findings disagree.

Skin scraping, microscopy and culture should answer a defined clinical question and be integrated with history, examination and the consequences of error. Explain uncertainty, record the sampling or observation conditions, and arrange a result-review plan rather than treating an isolated finding as self-interpreting.

Key points

  • Clean technique and correct site matter: collect scale from an active untreated border, affected nail from diseased depth, and abnormal hairs with roots or scalp scale.
  • Direct microscopy can provide earlier evidence of fungal elements, while culture supports identification but may take weeks and can be negative after treatment.
  • Stop or record recent topical and systemic antifungal exposure because it can reduce yield; never promise that a negative sample excludes infection.
  • Label patient, precise anatomical site and specimen type at the bedside, then use the laboratory container and transport process specified locally.
  • For Skin scraping, microscopy and culture, describe what is seen before assigning a diagnosis, and record site, extent, symptoms, duration and change over time.
  • A technically adequate result in Skin scraping, microscopy and culture can still be misleading when the wrong lesion, site, preparation or clinical question was selected.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Active scaly margin

Peripheral scale at an expanding annular edge is the highest-yield skin site for suspected dermatophyte infection.

Diseased nail depth

Subungual debris and abnormal proximal nail provide more useful material than distal free-edge clippings alone.

Scalp inflammatory patternRed flag

Patchy alopecia, scale, broken hairs or black dots suggests tinea capitis; boggy kerion needs prompt treatment to limit scarring.

Modified infection

Topical corticosteroid can suppress inflammation, distort a fungal border and create tinea incognito.

Alternative morphology

Exudate, follicular pustules, burrows or sharply geometric dermatitis may require bacterial, parasitic or contact-allergy assessment instead.

Red flags requiring action

  • Do not delay same-day assessment for severe pain, rapidly spreading infection, sepsis, orbital involvement, immunocompromise with extensive disease, or inflammatory scalp disease causing scarring alopecia.
03Method and interpretationA systematic approach to the test and its findings.
Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

  1. 01
    Direct microscopy of scale, hair or nailFirst step
    Why
    Look rapidly for fungal hyphae, spores or yeast forms.
    Interpretation and limitations
    A positive compatible finding supports mycosis; a negative result may reflect scant material, wrong site, prior treatment or reader limitations.
  2. 02
    Fungal culture
    Why
    Identify viable fungus when species or confirmation affects care.
    Interpretation and limitations
    Growth takes time and contaminants occur; interpret the named organism with specimen site, microscopy and clinical phenotype.
  3. 03
    Bacterial swab of exudate when indicated
    Why
    Assess secondary bacterial infection rather than dry scale.
    Interpretation and limitations
    Culture colonisation does not prove invasive infection, and cellulitis is usually diagnosed clinically rather than by an intact-skin swab.
  4. 04
    Repeat or alternative sampling
    Why
    Address persistent clinic-laboratory discordance before further treatment.
    Interpretation and limitations
    Repeat from a better untreated target, ask laboratory advice, or consider biopsy and alternative diagnoses instead of indefinite empirical therapy.
04Clinical next stepsHow the result changes management or prompts escalation.
01Planned assessmentUse mycology specimen collection systematicallyFirst stepThe patient is stable and the result will alter diagnosis, referral or follow-up.
  1. 1Define the question for Skin scraping, microscopy and culture, explain the process and obtain valid consent before exposing, touching, photographing or sampling skin.
  2. 2Choose representative anatomy, optimise lighting or specimen technique, and document site, morphology, symptoms and relevant previous treatment. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  3. 3Interpret the result beside the full clinical pattern, communicate uncertainty and arrange ownership of results and safety-netting. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
02Uncertain resultResolve discordance in Skin scraping, microscopy and cultureThe technical finding conflicts with the history, lesion evolution or wider examination.
  1. 1Recheck identity, site, timing, preparation, treatment exposure and whether the selected target was genuinely representative. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  2. 2Repeat or select a complementary test only when it can distinguish the remaining important alternatives. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  3. 3Seek dermatology, pathology, microbiology or allergy advice when clinicopathological disagreement would change urgent care. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
03Urgent patternDo not let mycology specimen collection delay escalationEscalationA rapidly progressive eruption, systemic illness, threatened vision or airway, or suspected aggressive malignancy is present. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  1. 1Stabilise immediate physiological threats and obtain same-day senior or specialty assessment according to the dominant emergency. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  2. 2DefinitiveTake time-critical images or specimens only when doing so will not postpone resuscitation, antimicrobials or definitive referral. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  3. 3Record evolution and communicate the differential, outstanding results and explicit deterioration triggers during handover. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
  • Record who will review the result arising from Skin scraping, microscopy and culture, the expected timescale and the action threshold before the patient leaves.
  • Compare subsequent findings with the original site description, dimensions, symptoms and image or specimen identifiers for Skin scraping, microscopy and culture.
  • Reassess earlier if rapid growth, bleeding, ulceration, fever, mucosal disease, eye symptoms or functional compromise develops. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
  • Document technical limitations and previous treatment that could alter sensitivity or specificity of mycology specimen collection.
  • Close the loop after specialist or laboratory review, including clinicopathological disagreement and any need for repeat sampling. Apply that step specifically within the skin scraping, microscopy and culture assessment and its recorded clinical context.
06Special situationsVariants, exceptions and circumstances that change the usual approach.

The edge contains activity

Dermatophytes expand centrifugally, so viable elements are more likely at a newly advancing scaly margin.

Nail clippings need depth

Large opaque distal fragments may yield less than crumbly subungual material taken toward active disease.

Microscopy and culture differ

Non-viable fungal elements can remain visible after treatment while culture requires growth from living organisms.

A label is clinical data

Left great toenail and scalp hair convey more interpretive value than a container labelled only skin.

Negative means conditional

A negative mycology result reduces probability only in proportion to specimen quality and timing.

07Common pitfallsFrequent interpretation and management errors.
  1. 01

    Scraping the smooth treated centre of an annular eruption while leaving the active border untouched.

  2. 02

    Submitting a dry swab for suspected fungus when adequate scale or nail material is available.

  3. 03

    Diagnosing bacterial cellulitis from colonising organisms grown from a chronic surface wound.

  4. 04

    Continuing repeated empirical antifungals after well-collected negative samples without reopening the differential.

  5. 05

    Failing to protect eyes and control sharps or blades while collecting airborne scale.

Practice

Two practice questions

Question 1 of 20 correct
DermatologyOriginal SBA

Best annular sampling site

A slowly enlarging annular plaque has peripheral scale and central clearing. No antifungal has been used. Where should material for mycology be collected?

Sources and review status3 sources · checked 27 Aug 2026 · clinical review pending
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom