Summary of Thyroid Blood Tests

This is a summary of the tests that we use for diagnosing thyroid disease. (1)

For screening for thyroid disease in patients who don’t have any symptoms:


For diagnosing hypothyroidism (an underactive thyroid) in patients with symptoms that suggest the disorder:

TSH—Above normal in thyroid problems (primary hypothyroidism) and below normal in 
 pituitary problems (secondary hypothyroidism).
                                                                                                                                         Antithyroglobulin antibodies and antithyroperoxidase antibodies—Above normal in patients  with Hashimoto’s thyroiditis (the most common cause of hypothyroidism).

For diagnosing hyperthyroidism (an overactive thyroid) in patients with symptoms that suggest the disorder:

TSH—Below normal except in the [very] rare case of a TSH secreting pituitary tumor.

Free T4 and Free T3—Above normal

Thyroid stimulating immunoglobulin; TSH receptor antibody–”usually (65%) positive in Graves disease” (2) (Graves disease is the cause of approximately 75% of overactive       
thyroid gland cases).

Normal Values

The normal levels of all these tests vary somewhat depending on the laboratory performing the test and so you will consult the lab’s normal values for each test.               

(1) Current Medical Diagnosis and Treatment, 2011. p.1062.

(2) Ibid.

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