General
Synonym/Acronym:
Free T4, FT4.
Common Use:
A complementary laboratory test in evaluating thyroid hormones levels related to deficiency or excess to assist in diagnosing hyperthyroidism and hypothyroidism.
Specimen:
Serum (1 mL) collected in a red- or tiger-top tube. Plasma (1 mL) collected in a green-top (heparin) tube is also acceptable.
Normal Findings:
(Method: Immunoassay)
| Age | Conventional Units | SI Units (Conventional Units × 12.9) |
|---|
| Newborn | 0.8–2.8 ng/dL | 10–36 pmol/L |
| 1–12 mo | 0.8–2 ng/dL | 10–26 pmol/L |
| 1–18 yr | 0.8–1.7 ng/dL | 10–22 pmol/L |
| Adult–older adult | 0.8–1.5 ng/dL | 10–19 pmol/L |
| Pregnancy (1st trimester) | 0.9–1.4 ng/dL | 12–18 pmol/L |
| Pregnancy (2nd trimester) | 0.7–1.3 ng/dL | 9–17 pmol/L |
Thyroxine, Free has been found in Davis's Lab & Diagnostic Tests
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