Diagnostic Relevance of the Lupus Band Test

Before interpreting a positive DIF finding in a presumed case of LE, several reasons for false-positive or false-negative results must be taken into account and excluded. Linear deposits or dust-like particles mostly containing IgM and/or C3 can be seen along the DEJ in a great variety of other inflammatory skin diseases - often in facial or chronically sun-exposed skin (Table 22.2). Continuous deposits of IgG, however, are usually not found in such cases and are conspicuous of true LE. In sun-protected nonlesional skin, DIF findings are always negative in biopsy specimens from patients with the diseases listed in Table 22.2. False-negative results can be obtained when fresh lesions or lesions from patients treated topically or systematically with corticosteroids or immunosuppressants are biopsied (Dahl 1983).

There is common understanding that a positive predictive or confirmatory value of the LBT in lesional skin for the diagnosis of LE is lower than the negative predictive value since a negative DIF finding in lesional skin is rather uncommon, whereas a (false-)positive DIF finding can be found in many other inflammatory skin diseases (Table 22.2). In nonlesional skin, however, a positive LBT result has a far higher positive predictive value than a negative one and clearly points to a diagnosis of LE, especially when deposits of IgG are present. Otherwise, the LBT, in lesional and unin-volved skin, has only little value for the distinction between DLE, SCLE, and SLE. For this purpose, serologic tests with demonstration of subtype-specific antinuclear antibodies are much more sensitive and specific (Conrad et al. 2000).

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