T3 uptake: Optimal Testing Recommendations

T3 uptake should not be used as a stand-alone test and has limited clinical utility.

Guidelines for Test Utilization

What does the test tell me?

T3 uptake estimates the amount of unoccupied binding sites on T4-binding proteins. This test should only be used to determine a free thyroxine index and has been replaced by more sensitive TSH and free T4 assays. [back to top]

When should I order this test?

Do not order this test. [back to top]

When should I NOT order this test?

This test should not be ordered, free T4 and TSH are better tests for the evaluation of hyper- and hypothyroidism. [back to top]

How should I interpret the result?

Values below the reference range are suggestive of hypothyroidism, values above the reference range are suggestive of hyperthyroidism. [back to top]

Is the test result diagnostic/confirmatory of the condition?

No, this test is not recommended for thyroid screening, free T4 and TSH should be used. [back to top]

Are there factors that can affect the lab result?

Heterophile antibodies and human anti-mouse antibodies (HAMA) that are present in specimens can interfere with accurate results (false negative or false positive results can occur). [back to top]

Are there considerations for special populations?

Pregnancy can increase thyroid binding globulin and that needs to be considered when calculating a free thyroxine index. [back to top]

What other test(s) might be indicated?

Free T4 and TSH should be used for routine thyroid screening. [back to top]


Alexander EK at al, 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid, 2017;27(3):315-389.

Hohnadel DC, et al., Hormones and their metabolites. In Clinical Chemistry Theory, Analysis and Correlation, eds Kaplan, LA and Pesce, AJ, 2nd edition, 1989, pp 961-962.

Last reviewed: March 2023. The content for Optimal Testing: the Association for Diagnostics & Laboratory Medicine’s (ADLM) Guide to Lab Test Utilization has been developed and approved by the Academy of Diagnostics & Laboratory Medicine and ADLM’s Science and Practice Core Committee.

As the fields of laboratory medicine and diagnostic testing continue to grow at an incredible rate, the knowledge and expertise of clinical laboratory professionals is essential to ensure that patients receive the highest quality and most useful laboratory tests. ADLM’s Academy and Science and Practice Core Committee have developed a test utilization resource focusing on commonly misused tests in hospitals and clinics. Improper test utilization can result in poor patient outcomes and waste in the healthcare system. This important resource geared toward medical professionals recommends better tests and diagnostic practices. Always consult your laboratory director to make sure these recommendations are appropriate for your patient population.