The current invention comprises a method for determining of an antibody against a drug antibody in a sample using an immunoassay comprising a capture drug antibody and a tracer drug antibody, wherein the method comprises providing i) a capture drug antibody, which is the drug antibody conjugated to a solid phase, ii) a tracer drug antibody, which is the drug antibody conjugated to a detectable label, contacting the capture drug antibody separately with i) the sample, ii) the sample, to which the drug antibody in monomeric form has been added, iii) the sample, to which the drug antibody in oligomeric form has been added, and determining an antibody against the drug antibody in the sample by a positive immunoassay in i) and a negative immunoassay in ii) and iii).