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TSH with Reflex to Free T4
Test Code36127
CPT Codes
84443
Includes
For patients 1 year of age or older, TSH will be performed first.
If it is abnormal (elevated or decreased) based on age/gender specific reference range, then a Free T4 will be performed at an additional charge (CPT code(s): 84439).
If it is abnormal (elevated or decreased) based on age/gender specific reference range, then a Free T4 will be performed at an additional charge (CPT code(s): 84439).
Preferred Specimen
1 mL serum
Patient Preparation
Specimen collection after fluorescein dye angiography should be delayed for at least 3 days. For patients on hemodialysis, specimen collection should be delayed for 2 weeks.
According to the assay manufacturer Siemens: "Samples containing fluorescein can produce falsely depressed values when tested with the Advia Centaur TSH3 Ultra assay."
Minimum Volume
0.7 mL
Instructions
This assay should only be ordered on patients 1 year of age or older. Orders on patients younger than 1 year will have a TSH only performed.
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days
Refrigerated: 7 days
Frozen: 28 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Plasma
Methodology
Immunoassay (IA)
Setup Schedule
Set up: Tues-Thurs, Sat; Report available: 2-5 days
Clinical Significance
This test may be useful in assessing thyroid dysfunction when pituitary disease is not suspected. In patients with clinical suspicion of hyperthyroidism or hypothyroidism, testing thyroid stimulating hormone (TSH) is the initial step [1]. An abnormal TSH result will reflex to a free thyroxine (T4) test to aid in diagnosis and guide further testing if needed.
TSH stimulates the thyroid gland to synthesize and secrete triiodothyronine (T3) and T4. TSH production is reduced in response to high T3/T4 levels and increased in response to low T3/T4 levels. When pituitary disease is not suspected, TSH serves as a sensitive marker for screening for thyroid dysfunction [1,2]. A normal TSH result excludes most cases of primary overt thyroid disease. When the TSH level is elevated, measurement of free T4 level may help diagnose subclinical or overt hypothyroidism. Thyroid peroxidase antibody testing may be needed to aid in the diagnosis of Hashimoto thyroiditis. When the TSH level is decreased, measurement of free T4 and free T3 may help identify hyperthyroidism or T3 thyrotoxicosis. In patients with thyrotoxicosis, TSH receptor antibodies testing helps confirm Graves disease [1-3].
Note: Interference due to heterophile antibodies has been known to occur [1].
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
References
1. Demers LM, et al. The thyroid: pathophysiology and thyroid function testing. In: Burtis CA, et al. eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed. Elsevier; 2006:2053-2095.
2. Ross DS, et al. Thyroid. 2016;26(10):1343-1421.
3. Vasileiou M, et al; Guideline Committee. BMJ. 2020;368:m41.
TSH stimulates the thyroid gland to synthesize and secrete triiodothyronine (T3) and T4. TSH production is reduced in response to high T3/T4 levels and increased in response to low T3/T4 levels. When pituitary disease is not suspected, TSH serves as a sensitive marker for screening for thyroid dysfunction [1,2]. A normal TSH result excludes most cases of primary overt thyroid disease. When the TSH level is elevated, measurement of free T4 level may help diagnose subclinical or overt hypothyroidism. Thyroid peroxidase antibody testing may be needed to aid in the diagnosis of Hashimoto thyroiditis. When the TSH level is decreased, measurement of free T4 and free T3 may help identify hyperthyroidism or T3 thyrotoxicosis. In patients with thyrotoxicosis, TSH receptor antibodies testing helps confirm Graves disease [1-3].
Note: Interference due to heterophile antibodies has been known to occur [1].
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
References
1. Demers LM, et al. The thyroid: pathophysiology and thyroid function testing. In: Burtis CA, et al. eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed. Elsevier; 2006:2053-2095.
2. Ross DS, et al. Thyroid. 2016;26(10):1343-1421.
3. Vasileiou M, et al; Guideline Committee. BMJ. 2020;368:m41.
