Thyroid peroxidase autoantibody immunoassay

A method of detecting an anti-thyroid peroxidase (anti-TPO) antibody in a biological sample from a subject, the method comprising:

• a) incubating in a reaction mixture,
• the biological sample from the subject with:
• a recombinant cynomolgus monkey thyroid peroxidase not conjugated to a label (unlabeled cynomolgus monkey rTPO), wherein the unlabeled cynomolgus monkey rTPO is directly or indirectly linked to a solid support, and
• a recombinant cynomolgus monkey thyroid peroxidase conjugated to a label (labeled cynomolgus monkey rTPO), wherein the labeled cynomolgus monkey rTPO is not linked to a solid support;
• wherein the label is selected from the group consisting of an enzyme conjugate, a fluorescent probe, a radioactive isotope, a chemiluminescent compound, and a bioluminescent compound;
• and
• b) detecting the presence or absence of a complex comprising the labeled cynomolgus monkey rTPO, the anti-TPO antibody, and the solid support, wherein the complex is formed by simultaneous binding of the anti-TPO antibody, if present in the sample, to the labeled cynomolgus monkey rTPO and the unlabeled cynomolgus monkey rTPO linked to the solid support, thereby linking the labeled cynomolgus monkey rTPO and the solid support;
• wherein the presence of the complex indicates the presence of the anti-TPO antibody in the biological sample.