What does the Total Triiodothyronine test measure?

Why is Total Triiodothyronine measured?

In a comprehensive thyroid panel, Total T3 provides a complementary measure of the full T3 pool alongside Free T3. Its primary clinical utility within the panel is in the assessment of T3 thyrotoxicosis — where T3 is disproportionately elevated relative to T4 — and as a secondary confirmatory marker of T3 status when Free T3 results appear inconsistent with clinical presentation. In routine functional medicine thyroid assessment, Free T3 is the clinically more informative marker as it reflects biologically active T3 independent of binding protein fluctuations; Total T3 adds interpretive value primarily in discordance scenarios.

Reference ranges

Standard reference

71–180 ng/dL (1.09–2.77 nmol/L) # REVIEWER FLAG: Confirm Access Medical Laboratories reference range for Total T3 and confirm whether Total T3 is included in the Thyroid Panel Comprehensive — some comprehensive panels include it alongside Free T3; others include only Free T3. If Total T3 is not included, remove this biomarker entry.

Functional medicine optimal

100–150 ng/dL (functional medicine mid-reference-range optimal). # REVIEWER FLAG: Not standardised in mainstream endocrinology — reviewer to confirm whether a Total T3 optimal range is clinically appropriate to document for this platform.

Units

ng/dL, nmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.