A thyroid panel consisting of thyroid stimulating hormone (TSH) and free thyroxine (fT4) should form the first line of diagnostic tests; tri-iodothyronine (T3) — total or free may be needed occasionally. A TSH assay capable of detecting levels below 0.02mIU/L is required to differentiate the suppressed TSH levels typical in Graves' disease from subnormal levels seen in some geriatric patients, non-thyroidal illness, and patients on medications. Additional tests including thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), and TSH receptor antibody (TRAb) may be ordered to enable differential diagnosis when indicated. Serum thyroglobulin (Tg) may serve as a tumour marker for monitoring patients with differentiated thyroid cancer.