Effective Test Utilization Recommendations

Do not routinely order Thyroid Hormone Binding Ratio (THBR, e.g., T3 Resin Uptake or T-Uptake) assays to determine the free T4 index. Use free T4 assays instead.

Chemistry

Before free T4 assays, the Thyroid hormone binding ratio (THBR) was part of a two-test procedure to estimate the free T4 index (FT4I). Modern FT4 assays are now faster, more accurate, and less expensive than this two-test index approach. When ordered with free T4, the THBR does not add value in routine evaluations. THBR retains limited utility in rare patients with inconsistent results attributed to the presence of abnormal binding proteins.

REFERENCES

Spencer CA. Laboratory thyroid tests: A historical perspective. Thyroid. 2023;33(4):407-419.
Guber HA, Farag AF. Evaluation of Endocrine Function. In: McPherson RA, Pincus MR. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 23rd Edition. St. Louis: Elsevier, Inc; 2017.

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