Tissue biopsies, including immunofluorescence examination

Role

Tissue biopsy with immunofluorescence detects antibody, complement, or immune complex deposition in tissue - central to diagnosing autoimmune skin, renal, and other organ disease where routine histology alone is insufficient
Two main techniques: direct immunofluorescence (DIF) - detects antibody/complement already deposited in the patient's own biopsied tissue; indirect immunofluorescence (IIF) - detects circulating autoantibodies in the patient's serum by applying it to a substrate tissue

DIF requires a fresh/frozen (not formalin-fixed) specimen, often taken from perilesional rather than lesional skin for blistering disorders (lesional tissue may show non-specific inflammatory destruction of the antigen being sought)
IIF substrate choice matters - e.g. Hep-2 cells for ANA pattern, monkey oesophagus for anti-desmoglein antibodies in pemphigus

Pattern	Classic association
Linear IgG/C3 along the basement membrane	Bullous pemphigoid
Intercellular ("chicken-wire") IgG	Pemphigus vulgaris
Granular IgA at the dermal papillary tips	Dermatitis herpetiformis (coeliac-associated)
Granular IgG/IgM/C3 ("full house")	Lupus nephritis
Linear IgG along the glomerular basement membrane	Anti-GBM disease (Goodpasture's)

Correct specimen handling (fresh/frozen for DIF, correct transport medium) is essential - an inadequately handled specimen cannot be salvaged, unlike routine histology, which tolerates formalin fixation

Bullous pemphigoid, pemphigus vulgaris, dermatitis herpetiformis, lupus nephritis, anti-GBM disease

The specific immunofluorescence pattern often narrows the diagnosis more precisely than clinical appearance alone, particularly for distinguishing the blistering disorders from one another

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