| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
TSH with Reflex to Free T4 : 36127
Test CodeTSH3RC or 36127
Alias/See Also
Thyroid Stimulating Hormone with Reflex
CPT Codes
84443; If reflex add 84439
Includes
TSH; 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, a Free T4 will be performed at an additional charge (CPT code: 84439)
Instructions
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.
Transport Container
Specimen:
1 mL serum
Minimum Volume: 0.7 mL
1 mL serum
Minimum Volume: 0.7 mL
Transport Temperature
Room temperature.
Specimen Stability
Room temperature: 7 days; Refrigerated: 7 days; Frozen: 28 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Plasma
Methodology
Immunoassay
Setup Schedule
Sunday - Saturday
Report Available
1 day
Limitations
According to the assay manufacturer Siemens: "Samples containing fluorescein can produce falsely depressed values when tested with the Advia Centaur TSH3 Ultra assay."
Reference Range
TSH:
Premature Infants (28-36 Weeks)
1st Week of Life 0.20-27.90 mIU/L
Term Infants (>37 Weeks)
Serum or Cord Blood 1.00-39.00 mIU/L
1-2 Days 3.20-34.60 mIU/L
3-4 Days 0.70-15.40 mIU/L
5 Days-4 Weeks 1.70-9.10 mIU/L
1-11 Months 0.80-8.20 mIU/L
1-19 Years 0.50-4.30 mIU/L
≥20 Years 0.40-4.50 mIU/L
Pregnancy
First Trimester 0.26-2.66 mIU/L
Second Trimester 0.55-2.73 mIU/L
Third Trimester 0.43-2.91 mIU/L
TSH levels decline rapidly during the first week of life in most children, but may remain transiently elevated in a few individuals despite normal free T4 levels. For proper interpretation of an abnormal TSH from a newborn thyroid screen, a Total T4 (test code 867) should be considered.
For patients 1 year of age or older, Free T4 will be performed when TSH result exceeds age/gender specific reference range.
If reflex to Free T4:
<1 Month Not established
1-23 Months 0.9-1.4 ng/dL
2-12 Years 0.9-1.4 ng/dL
13-20 Years 0.8-1.4 ng/dL
>20 Years 0.8-1.8 ng/dL
Premature Infants (28-36 Weeks)
1st Week of Life 0.20-27.90 mIU/L
Term Infants (>37 Weeks)
Serum or Cord Blood 1.00-39.00 mIU/L
1-2 Days 3.20-34.60 mIU/L
3-4 Days 0.70-15.40 mIU/L
5 Days-4 Weeks 1.70-9.10 mIU/L
1-11 Months 0.80-8.20 mIU/L
1-19 Years 0.50-4.30 mIU/L
≥20 Years 0.40-4.50 mIU/L
Pregnancy
First Trimester 0.26-2.66 mIU/L
Second Trimester 0.55-2.73 mIU/L
Third Trimester 0.43-2.91 mIU/L
TSH levels decline rapidly during the first week of life in most children, but may remain transiently elevated in a few individuals despite normal free T4 levels. For proper interpretation of an abnormal TSH from a newborn thyroid screen, a Total T4 (test code 867) should be considered.
For patients 1 year of age or older, Free T4 will be performed when TSH result exceeds age/gender specific reference range.
If reflex to Free T4:
<1 Month Not established
1-23 Months 0.9-1.4 ng/dL
2-12 Years 0.9-1.4 ng/dL
13-20 Years 0.8-1.4 ng/dL
>20 Years 0.8-1.8 ng/dL
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.
Performing Laboratory
med fusion
