Synopsis
Choose, consent, collect and transport skin for direct immunofluorescence, interpret major deposit patterns in clinical context, and route blistering, vasculitic and connective-tissue presentations to the right urgency of specialist care.
- Direct immunofluorescence detects immunoglobulin, complement or fibrin deposited in the patient's skin; it is different from routine H&E histology and indirect immunofluorescence performed on serum.
- Autoimmune blistering investigation usually needs two separately selected punch biopsies: a fresh blister edge or lesional sample in formalin for H&E and intact perilesional skin in the laboratory's fluorescence transport system for DIF.
- For dermatitis herpetiformis, choose normal-appearing skin immediately beside a fresh lesion; eroded, excoriated or directly involved tissue can lose the diagnostic granular IgA signal.
- Suspected cutaneous small-vessel vasculitis needs a very fresh lesion for DIF and a separately selected developed lesion for morphology, with timing and site agreed locally.
- Never put the DIF specimen into formalin. Michel transport medium is commonly used, but the receiving laboratory's current medium, temperature, courier and time limits govern the collection.
- Linear IgG and C3 along the basement membrane supports pemphigoid; intercellular epidermal IgG supports pemphigus; granular IgA at dermal papillary tips supports dermatitis herpetiformis.
- A negative DIF does not exclude disease when the site was eroded, the lesion was old, treatment preceded biopsy, transport failed or the clinical condition has imperfect sensitivity.
- Explain why one or two scars may be needed, discuss bleeding, infection, wound care and result ownership, and label every pot with exact site, lesion age, medium and intended test.
- Same-day referral is driven by clinical severity, not by waiting for DIF; stable localised suspected autoimmune blistering still deserves prompt dermatology assessment before prolonged empirical corticosteroid treatment.
Key red flags
Rapid spread, Nikolsky-positive or painful skin, fever, hypotension, extensive erosions, eye pain or visual change, dysphagia, reduced intake or urine, breathing symptoms, genital involvement, immunosuppression or a vulnerable age group requires urgent specialist triage before routine biopsy booking.
Pain, flat duskiness, detachment, fever or multi-site mucositis points to an emergency drug reaction or other severe disease in which referral precedes an elective test pathway.
Investigation priorities
Define the leading disease, choose lesion age and preserve a record for clinicopathological correlation.
Management branches
A blistering, erosive, purpuric or interface eruption may need immunofluorescence.
- Assess observations, skin pain and extent, hydration, infection, mouth, eyes, genital and airway involvement and systemic renal, gastrointestinal, neurological or respiratory features.
- Arrange emergency admission and dermatology review for instability or threatened epithelium and begin time-critical supportive or disease-directed care without waiting for an ideal specimen.
- For stable disease, contact dermatology promptly, state the leading differential and agree tissue, serum, treatment timing and referral urgency before booking an undirected biopsy.
H&E and DIF are both needed to investigate a stable patient.
- Explain that the specimens test different tissue features and may require two sites, then discuss local anaesthetic, pain, bleeding, infection, scar, pigment change, stitches, photographs and the option to decline.
- Review allergies, bleeding history, anticoagulants, healing risk and aftercare without stopping prescribed antithrombotic treatment unless the responsible clinical protocol advises it.
- Mark and photograph each intended site with consent, prepare pre-labelled formalin and laboratory-specified DIF containers and record who will communicate results and remove sutures.