Triiodothyronine (T3), Total, Serum


See Also Free Thyroxine (FT4), Serum


T3 testing is ordered primarily to help diagnose hyperthyroidism and may be ordered to help monitor the progress of a patient with a known thyroid disorder. The T3 test is usually ordered following an abnormal TSH and T4 test. Either the total T3 or the free T3 may be ordered. Since most of the T3 is bound to protein, the total T3 can be affected by protein levels and protein binding ability, but the free T3 is not. Moreover, free T3 is the biologically active form of the hormone.

Sample Type, Quantity & Conditions

1 ml Serum 1 ml Li, Na, NH4+-Heparin, K3-EDTA, Sodium Citrate, or Sodium Fluoride/Potassium Oxalate Plasma Stability: 7 Days at 2-8 °C 1 Month at -20 °C

Special Precautions

Indicate T3 total to avoid confusion with free T3.

Normal Range

0.89 -2.44 nmol/L

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