Sensitivity of Immunofluorescence Studies vs Enzyme-Linked Immunosorbent Assay for Diagnosis of Bullous Pemphigoid

We read with interest the Practice Gap comments of Dr Chan published in the March issue of the Archives.¹ We agree that there is a lack of consensus on diagnostic criteria for bullous pemphigoid (BP) and a need to provide better information in this area. However, the author's recommendation to routinely perform the commercially available enzyme-linked immunosorbent assay (ELISA) for BP180 instead of using indirect immunofluorescence (IIF) microscopy studies on a split-skin sample for the diagnosis of BP cannot be fully supported.

The first question to address is whether characterization of circulating autoantibodies is required to establish the diagnosis of BP. This is not the case, since clinical features are sufficient to make the diagnosis of BP in patients with positive direct immunofluorescence findings.² Previous studies have shown that when 3 of 4 clinical criteria are present, the diagnosis of BP can be made with a sensitivity of 90%, a specificity of 83%, and a high positive predictive value.² Hence, the routine performance of the ELISA for BP180 represents an academic diagnostic exercise. Interestingly, a minor adaptation of the direct immunofluorescence microscopy technique with analysis of the fluorescence pattern ( “n ” and “u ” serrated patterns) would also allow the clinician to rapidly and easily distinguish BP from other conditions with almost no extra costs or blood sampling.³

Second, there are a minority of studies^{4 - 6} (Table) that have shown ELISA for BP180 to be a more sensitive test than IIF for BP. The recently reported low sensitivity of IIF (62%) was owing to the use of monkey esophagus, which is not the substrate of reference for the search of BP autoantibodies.⁴ As a matter of fact, because selected serum samples were used, most studies have overestimated the sensitivity of commercially available ELISAs. In the only prospective study available to our knowledge, our research group found that findings in ELISA for BP180 and IIF studies using split-skin samples were comparable.¹⁵

In another retrospective study of 190 patients, positive findings in ELISA for BP180 and IIF using split-skin samples were found in 79% and 81% of cases, respectively.¹⁸ Even if ELISA for BP180 has advantages (eg, multiple sample testing, ease of performance, standardization), the commercially available kits cost $46.00 to $65.00 per test. Furthermore, ELISA for BP180 does not provide clues for specific conditions, such as p200 pemphigoid or epidermolysis bullosa acquisita. Of note, a recent prospective study¹⁹ has provided evidence that ELISA for BP180 should be performed at the time of cessation of therapy as a prognostic test (rather than a diagnostic test). In fact, patients with increased BP180 values found on ELISA have an increased risk for relapse.

Finally, since the combination test of ELISA for BP180 and the newly available ELISA for BP230 only slightly increases the diagnostic sensitivity (plus 5% to 10%) achieved with ELISA for BP180 alone, ELISA for BP230 should be performed only in the subset of patients with negative ELISA findings for BP180.^{4 ,18}

In conclusion, (1) the diagnosis of BP can be made with high sensitivity and specificity based on certain clinical features when direct immunofluorescence study findings are positive; (2) the ELISA for BP180 (NC16A, MBL Co) does not have a higher sensitivity than salt-split skin IIF studies for the diagnosis of BP; and (3) its usefulness in the management of patients during the decrease of corticosteroid doses remains to be demonstrated.