Laboratory Medicine
Test Directory / Free T3
Free T3
Brown clotted serum, gel barrier
| Test | Free T3 |
|---|---|
| Common Abbreviations | FT3 |
| Profile | NA |
| Tube type | Brown clotted serum, gel barrier |
| Clinical Indication | FT3 is especially useful in the diagnostic differentiation between euthyroid, hyperthyroid and hypothyroid individuals.FT3 levels correlate with T3 secretion and metabolism. In hypothyroidism and hyperthyroidism, FT3 levels parallel changes in total T3 levels. Measuring free T3 is useful when altered levels of total T3 occur due to changes in T3 binding proteins, especially TBG. TBG levels remain relatively constant in healthy individuals, but certain conditions, such as pregnancy and steroid therapy, can alter these levels. In these conditions, FT3 levels are unchanged, while total T3 levels parallel the changes in TBG. |
| Specimen Type | Blood |
| Sample type | Serum |
| Minimum Volume | 0.5mL If requesting more than 10 tests please send an additional brown clotted serum sample. |
| Special Precautions | No special requirements |
| Stability | 5 days at 20 - 25°C, 7 days at 2 - 8°C and 30 days at -20°C |
| Turnaround Time | Inpatient: 24 hours Outpatient/ GP: 24 hours |
| Laboratory | York and Scarborough |
| Reference Interval | 0 - 6 Days: 2.7 - 9.7 pmol/L 7 Days - 3 Months: 3.0 - 9.3 pmol/L 3 Months -12 Months: 3.3 -9.0 pmol/L 1 Year 6 Years: 3.7 8.5 pmol/L 7 Years 11 Years: 3.9 8.0 pmol/L 12 Years 20 Years: 3.9 7.7 pmol/L Adults: 3.1 6.8 pmol/L 1st Trimester: 3.8 6.0pmol/L 2nd Trimester: 3.2 5.5 pmol/L 3rd Trimester: 3.1 5.0 pmol/L (Quoted by the manufacturer) |
| Limitations | Analysis should not be performed on haemolysed, icteric or lipaemic samples. The assay is unaffected by biotin < 4912 nmol/L or < 1200 ng/mL. No interference was observed from rheumatoid factors up to a concentration of 1200 IU/mL. No interference was observed from IgG < 7.0 g/dL; IgA < 1.6 g/dL; IgM < 1.0 g/dL In vitro tests were performed on 17 commonly used pharmaceuticals. No interference with the assay was found. In addition, special thyroid drugs were tested. No interference was found. Any influence that might affect the binding behaviour of the binding proteins can alter the result of the fT3 tests (e.g. drugs, Non-Thyroid Illness or patients suffering from Familial Dysalbuminemic Hyperthyroxinemia). In rare cases, interference due to extremely high titres of antibodies to analyte specific antibodies, streptavidin or ruthenium can occur. |
| Notes |
