What is the role of direct immunofluorescence (DIF) studies in the diagnosis of bullous pemphigoid (BP)?

Updated: Oct 14, 2020
  • Author: Lawrence S Chan, MD; Chief Editor: Dirk M Elston, MD  more...
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DIF studies demonstrate in vivo deposits of antibodies and other immunoreactants, such as complement. DIF tests usually demonstrate IgG (70-90% of patients) and complement C3 deposition (90-100% of patients) in a linear band at the dermal-epidermal junction. This pattern of immunoreactants is not specific for bullous pemphigoid and may be seen in cicatricial pemphigoid and epidermolysis bullosa acquisita. Bullous pemphigoid can be differentiated from these conditions by incubating the patient's skin biopsy sample in 1 mol/L salt prior to performing the DIF technique. This process induces cleavage through the lamina lucida. DIF on salt-split skin reveals IgG on the blister roof (epidermal side of split skin) in patients with bullous pemphigoid, while, in CP and EBA, the IgG localizes to the blister floor (dermal side of split skin).

The optimal location for DIF testing is normal-appearing perilesional skin. False-positive results can be observed when it is performed on lesional skin. There is a significant false-negative rate if the skin biopsy specimen is taken from skin of the legs. [3] Rarely, skin biopsy samples placed in transport media may yield false-negative results. This observation makes the use of fresh tissue the preferred substrate for DIF studies. See the image below.

Direct immunofluorescence study performed on a per Direct immunofluorescence study performed on a perilesional skin biopsy specimen from a patient with bullous pemphigoid detects a linear band of immunoglobulin G deposit along the dermoepidermal junction.

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