Herein is reported an enzyme linked immunosorbent assay for the detection of anti-drug antibodies against a drug antibody in a sample comprising a capture drug antibody and a tracer drug antibody, wherein the capture drug antibody and the tracer drug antibody are employed in a concentration of 0.5 μg/ml or more, the sample is incubated simultaneously with the capture drug antibody and the tracer drug antibody for 1 to 24 hours, the capture drug antibody and the tracer drug antibody are derivatized via a single lysine residue, the sample comprises 10% serum, and oligomeric human IgG is added to the sample prior to the incubation with the capture drug antibody and the tracer drug antibody.