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Thyroxine
Test CodeT4
CPT Codes
84436
Preferred Specimen
1.0 mL collected in a SST (serum seprator-gold top tube)
Minimum Volume
0.5 mL
Other Acceptable Specimens
Plasma - Li Heparin (PST) Plasma –EDTA (Lavender) Gold top (SST) Tiger top (SST) Red top
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 4 days at 20-24ºC
Refrigerated: 8 days at 2-8°C
Frozen: 12 months at -20°C, Freeze only once.
Refrigerated: 8 days at 2-8°C
Frozen: 12 months at -20°C, Freeze only once.
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Samples not labeled with complete first and last name and date of birth.
Grossly hemolyzed.
Grossly hemolyzed.
Methodology
Electrochemiluminescence Immunoassay
Setup Schedule
Sun - Sat
Report Available
Same day
Reference Range
4.50 – 11.70 ug/dL
Clinical Significance
The hormone thyroxine (T4) is the main product secreted by the thyroid gland and is an integral
component of the hypothalamus-anterior pituitary-thyroid regulating system. It has the function of anabolically influencing metabolism. Thyroxine is formed in a coupling reaction from two DIT molecules (3,5-diiodotyrosine) in the thyroid gland. It is stored bound to thyroglobulin in the lumina of the thyroid follicles and is secreted as required under the influence of TSH.
The major part (> 99 %) of total thyroxine (T4) in serum is present in protein-bound form. As the concentrations of the transport proteins in serum are subject to exogenous and endogenous effects, the status of the binding proteins must also be taken into account in the assessment of the thyroid hormone concentration in serum. If this is ignored, changes in the binding proteins (e.g. due to estrogen-containing preparations, during pregnancy or in the presence of a nephrotic syndrome etc.) can lead to erroneous assessments of the thyroid metabolic state.
The determination of T4 can be utilized for the following indications: the detection of hyperthyroidism, the detection of primary and secondary hypothyroidism, and the monitoring of TSH-suppression therapy.
component of the hypothalamus-anterior pituitary-thyroid regulating system. It has the function of anabolically influencing metabolism. Thyroxine is formed in a coupling reaction from two DIT molecules (3,5-diiodotyrosine) in the thyroid gland. It is stored bound to thyroglobulin in the lumina of the thyroid follicles and is secreted as required under the influence of TSH.
The major part (> 99 %) of total thyroxine (T4) in serum is present in protein-bound form. As the concentrations of the transport proteins in serum are subject to exogenous and endogenous effects, the status of the binding proteins must also be taken into account in the assessment of the thyroid hormone concentration in serum. If this is ignored, changes in the binding proteins (e.g. due to estrogen-containing preparations, during pregnancy or in the presence of a nephrotic syndrome etc.) can lead to erroneous assessments of the thyroid metabolic state.
The determination of T4 can be utilized for the following indications: the detection of hyperthyroidism, the detection of primary and secondary hypothyroidism, and the monitoring of TSH-suppression therapy.
Performing Laboratory
Frederick Health Laboratory
400 W 7th Street
Frederick, MD 21701
Last Updated: November 1, 2024
