The reference range for thyroid peroxidase antibodies (TPO) has changed since my previous test. Why is this?

Why has the reference range changed?

Our partner laboratory is using a new assay for the thyroid peroxidase (TPO) antibody test. This updated method is more sensitive and better standardised for detecting TPO antibodies.

Reference ranges are specific to the testing method used and are established using healthy population studies and clinical research. Because of this, reference ranges can vary slightly when laboratories adopt new assays.

Is my previously negative result now considered positive?

No. If a previous result was reported as negative, it remains negative.

The reference range that applied at the time of testing is the correct one for interpreting that result. The previous and new laboratory assays are not directly interchangeable, so results from the two methods should not be compared using the same reference range.

Can this change affect my diagnosis or treatment?

For most people, this change will not affect diagnosis or treatment.

TPO antibodies are only one part of assessing thyroid health. Doctors also consider your symptoms and thyroid hormone tests when making clinical decisions.