Background: A variety of thyroid antibody assays are used in the diagnosis of auto-immune thyroid disease (AITD). Commonly both thyroid peroxidase (TPOab) and thyroglobulin antibodies (TGab) are measured but the added value of testing two markers has not been established.
Method: We retrospectively collected clinical and laboratory data on 500 consecutive patients who had thyroid autoantibodies requested from a specialist endocrine department of a tertiary hospital from December 2008 to October 2010. TPOab and TGab were simultaneously analysed using the FIDIS multiplex bead assay (BMD, Marne La Vallee, France).
Results: There were 399 (79.8%) females and 101 (20.2%) males in the cohort, aged 43.5±15.3 (mean±SD) years. 163 (32.6%) patients had Graves disease and 118 (23.6%) had Hashimotos thyroiditis. The other diagnoses included; thyroid nodules 101 (20.2%), other autoimmune diseases e.g. type 1 diabetes 58 (11.6%), primary hypothyroidism 41 (8.2%) and transient thyroiditis 19 (3.8%). From the 163 patients with Graves disease 107 (65.6%) had TPOab, 64 (39.3%) had TGab. Of the 118 patients with Hashimotos thyroiditis, 103 (87.3%) were positive for TPOab and 73 (61.9%) positive for TGab.
|TPO only||TPO and TG||TG only||Both negative|
|Graves||53 (32.5%)||50 (30.6%)||14 (8.6%)||46 (28.2%)|
|Hashimotos||44 (37.3%)||60 (50.8%)||14 (11.9%)||0|
Conclusion: TPOab testing was superior to TGab assay in identifying patients with both Graves disease and Hashimotos thyroiditis. Although there may be a rationale in reserving TGab testing as a second-line test in patients testing negative for TPOab, this would miss 8.6% of Graves and 11.9% of Hashimotos thyroiditis patients. The multiplex assay tests both antibodies concurrently and dual testing provides increased sensitivity for AITD. The higher cost of the multiplex assay would be offset by the need to test TGab separately in the anti-TPO negative patients, which constitute 34.4% of Graves disease and 12.7% of Hashimotos patients.