The Detection of Anti-adalimumab Antibodies in a Series of Inflammatory Polyarthritis: three ELISA Methods Compared.

Background: A reliable identification of ADAb represents a fundamental tool in the followup of patients under treatment with anti-TNF drugs.

Objectives: To compare three immunoenzymatic assays for anti-adalimumab antibodies (AAA) detection.

Methods: The study was performed in 40 patients with chronic inflammatory polyarthritis, comprising both patients showing a good response to adalimumab (ADL) and patients who lost response or did not respond to ADL, recently or in the past (retrospective study). Thus, sera were collected before ADL administration or well after ADL discontinuation. AAA were analysed by three different bridging ELISAs, following manufacturers' instructions.

Results: All methods disclosed negative results in responder patients and univocally recognized 11/31 (35.5%) AAA highpositive samples in non-responder patients, including several cases that had discontinued ADL for a long time (range 3-48 months). Among the overall non-responder patients, 10/31 (32.3%) disclosed concordant clear-cut AAA-negative results, while negative versus low-positive or borderline results were found in another ten non-responder patients, indicating slight differences in sensitivity between the methods, especially in patients who were analysed retrospectively. Methotrexate in combination therapy with ADL tended to be more frequent in AAA-negative, than in AAA-positive patients (52.6% vs. 25%; p=ns).

Conclusions: The three bridging ELISA methods under study showed a good agreement and were able to identify uniquely the presence of high positive AAA, even after a long time since ADL discontinuation.