TSH receptor antibodies (TRAb)

Cut-offs depend on the assay (for example below 1.75, below 1.0 or below 0.4 IU/L, and some TSI assays print a ratio or a percentage), so the lab's own printed cut-off is the one to use.

TSH receptor antibodies are immune proteins that attach to the same switch on thyroid cells that TSH normally uses. In Graves disease they stimulate the switch and make the thyroid overactive; less often they block it. The test measures how much of this antibody is in the blood.

It is requested to find out whether an overactive thyroid is caused by Graves disease rather than nodules or thyroiditis, in pregnancy where Graves disease is known or suspected, and sometimes to help judge whether the condition has settled after a course of anti-thyroid tablets.

• Graves disease, the commonest cause of an overactive thyroid in younger adults
• Thyroid eye disease
• Occasionally in autoimmune underactive thyroid disease, with blocking antibodies
• Levels tend to be higher early in Graves disease and can fall with treatment

• A value below the cut-off is the expected finding
• Falling levels during and after a course of anti-thyroid tablets
• Remission of Graves disease
• Some assays are less sensitive than others

• A small proportion of healthy people have a low positive result
• Different assays measure slightly different things (TRAb, TBII, TSI) and give different numbers
• Biotin supplements can interfere on some analysers

No fasting needed. In Graves disease doctors sometimes repeat it towards the end of a course of tablets, and in pregnancy at set points, to inform planning.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.