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T4, Total

Item Value
Available Stat? No
Test code TT4
Test group Thyroid tests
Performed by Quest
Sendout? Yes
Method Immunoassay
Collection Instructions Indicate testing is for pregnant patient on requisition.
Container type Gold top
Amount to Collect 2 mL blood
Sample type Serum
Preferred volume 1 mL serum
Min. Volume 0.5 mL serum
Processing notes Store at room temperature. Order Quest # 17733
Units µg/dL (mcg/dL)
Normal range
1-8 Years 5.9-11.5 mcg/dL
9-13 Years 4.7-10.4 mcg/dL
14-17 Years 5.0-9.8 mcg/dL
≥ 18 year old 4.8-10.4 mcg/dL

1st Trimester 6.4-15.2 mcg/dL
2nd Trimester 7.4-15.2 mcg/dL
3rd Trimester 7.7-13.8 mcg/dL
All Trimesters Together 7.0-14.7 mcg/dL
Synonyms thyroxine; tetraiodothyronine
Stability Room temperature 7 days, refrigerated 7 days, frozen at -20C 1 month.
Turn around times Test run Monday-Friday AM. Results available 1-2 days.
Additional information Conversion: 1 µg/dL = 12.9 nmol/L

Clinical significance: Thyroxine (T4) is the major secretory hormone of the thyroid. Only 0.03% of T4 is unbound and free for exchange with tissues. Thyroid function may be assessed with thyroid stimulating hormone (TSH) and free T4 measured.

Although free T4 is generally preferred over total T4 when monitoring thyroid function, the total T4 measurement may be preferred for monitoring of pregnant patients where total T4 reference ranges are available. The total T4 concentrations tend to be stable throughout pregnancy at 150% of the values in non- pregnant subjects and can be useful when the levels are evaluated according to pregnancy specific total T4 reference ranges which are approx. 1.5 times greater than non-pregnant ranges.

Reference: Mandel SJ, Spencer CA, Hollowell JG., Are detection and treatment of thyroid insufficiency in pregnancy feasible?Thyroid. 2005 Jan;15(1):44-53.
CPT coding 84436-90
LOINC code 3026-2
Last Updated 6/14/2016 3:10:04 PM
Entry Number 918
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