TSH with Reflex to FT4

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NEW YORK DOH APPROVED: YES

CPT Code: 84443

Order Code: C513

For patients 1 year of age or older, Free T4 will be performed at an additional charge (CPT code 84439) when TSH result exceeds age specific reference range.

ABN Requirement:  No
Synonyms: Thyroid Stimulating Hormone with Reflex
Specimen: Serum
Volume: 1.0 mL
Minimum Volume: 0.7 mL
Container: Gel-barrier tube (SST)

Collection:

1. Collect and label sample according to standard protocols.
2. Gently invert tube 5 times immediately after draw. Do not shake.
3. Allow blood to clot 30 minutes.
4. Centrifuge for 10 minutes.

Special 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. According to the assay manufacturer Siemens: “Samples containing fluorescein can produce falsely depressed values when tested with the Advia Centaur TSh4 Ultra assay.”

Transport: Store serum at 2°C to 8°C after collection and ship the same day per packaging instructions included with the provided shipping box.

Stability:

Ambient (15-25°C): 7 days
Refrigerated (2-8°C): 7 days
Frozen (-20°C): 28 days

Causes of Rejection: Specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits

Methodology: Immunoassay (IA)

Turn Around Time: 1 to 3 days

Reference Range:

Thyroid Stimulating Hormone (TSH): See individual test

Thyroxine (T4), Free: See individual test

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.

The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.

Determination of optimal TSH ranges for reflex Free T4 testing

CLINICAL THYROIDOLOGY FOR THE PUBLIC
A publication of the American Thyroid Association

Summaries for the Public from recent articles in Clinical Thyroidology

Table of Contents | PDF File for Saving and Printing

THYROID HORMONE TESTS
Determination of optimal TSH ranges for reflex Free T₄ testing

BACKGROUND
TSH measurement is generally regarded as the most sensitive initial laboratory test for screening individuals for thyroid hormone abnormalities. This is due to the fact that small changes in Free T₄ levels result in larger changes in TSH values. Many clinicians and laboratories check TSH alone as the initial test for thyroid problems and then only add a Free T₄ measurement if the TSH is abnormal (outside the laboratory normal reference range). When the laboratory adds the Free T₄ test to the blood sample automatically based on an abnormal TSH result, it referred to as “reflex” testing. Although laboratories vary, most report a normal TSH reference range between 0.4-0.5 mU/L on the lower end and 4-5.5 mU/L on the upper end of the range. The goal of this study was to evaluate different TSH cutoffs leading to reflex Free T₄ testing, with the purpose to determine whether a widened normal range could decrease the need for additional Free T₄ testing and not lead to missing cases of thyroid problems.

THE FULL ARTICLE TITLE:
Henze M et al. Rationalizing thyroid function testing: Which TSH cutoffs are optimal for testing Free T4?. J. Clin Endocrinol. Metab. 2017. 102 (11): 4235-4241.

SUMMARY OF THE STUDY
These investigators evaluated TSH and Free T₄ measurements in two populations. One group of 120,403 individuals (named the clinical group) had thyroid tests performed in a single laboratory in Western Australia over a 12 year period of time. This group was compared to community group of 4568 individuals participating in the Busselton Health Study. All individuals had both TSH and Free T₄ measured. They excluded people with known pituitary disease, thyroid disease and other factors known to affect thyroid function tests. These investigators quantified the number of individuals at different TSH values that had high, low or normal Free T₄ levels. They measured the effect of changing the TSH reference range cutoffs on the number of reflex Free T₄ tests. They determined how many times an abnormally high or low Free T₄ would have gone undetected if the TSH cutoffs for reflex testing had been changed. The normal reference range for the TSH was 0.4-4 mU/L in this study. They found in the clinical group that if the TSH normal range that led to reflex Free T₄ testing was changed to from 0.4-4 mU/L to 0.3-5 mU/L, this would have led to a 22% reduction in the number of Free T₄ tests performed. As expected, if the TSH normal reference range was widened even more to 0.2-6 mU/L, even fewer reflex Free T₄ tests would have been done.

They then examined how many of those Free T4 levels that would not have been done were abnormal. When the TSH lower limit was reduced from 0.4 to 0.2 mU/L, a high Free T₄ would have been missed in 4.2% of people who had a TSH between 0.2 and 0.4 mU/L. When the TSH upper limit was raised from 4 to 6 mU/L, a low Free T₄ would have been missed in 2.5% of the people who had a TSH between 4 and 6 mU/L.

The authors noted that this was a relatively small number of people that would have been missed and that the majority had only very slight abnormalities of Free T₄. They suggested that these mild abnormalities were unlikely to be associated with clinically important overt hyper- or hypothyroidism. The vast majority of people (97%) with a TSH in the normal range of 0.4-4 mU/L also had normal Free T₄ values. The findings were similar but of lesser magnitude in the smaller community group of patients. The authors concluded that the TSH reference range leading to reflex Free T₄ testing could likely be widened to decrease the number of unnecessary Free T₄ measurements performed. This would reduce overall costs to the medical system without likely causing negative consequences in terms of missing the detection of people with thyroid hormone abnormalities.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?

These results indicate that by widening the normal reference range for TSH, the need for additional reflex testing for Free T₄ values could be reduced. The authors suggested that fewer unnecessary Free T₄ measurements would be performed and thus these changes would be cost saving for the health care system. The results indicated that the TSH normal reference range could be altered with minimal clinical effects. In other words, few cases of overt hyper- or hypothyroidism would go undetected if the TSH cutoffs leading to reflex Free T₄ testing were only slightly changed. It is important to note, that this study refers to the finding of overt thyroid disease and does not address the concept of “subclinical” or mild thyroid disorders. Additionally it is important to remember that TSH testing alone is inadequate or misleading in some conditions (such as central hypothyroidism or other abnormal thyroid conditions). This study primarily addresses the utility of isolated TSH measurements when screening people for new thyroid disease. When screening the general population for thyroid disease, the majority of people with a TSH in the normal reference range will also have a normal Free T₄, making the new diagnosis of a thyroid disorder unlikely when a person has a normal TSH.

— Whitney W. Woodmansee MD

ATA THYROID BROCHURE LINKS

Thyroid Function Tests: https://www.thyroid.org/thyroid-function-tests/

Hypothyroidism (Underactive): https://www.thyroid.org/hypothyroidism/

Hyperthyroidism (Overactive): https://www.thyroid.org/hyperthyroidism/

ABBREVIATIONS & DEFINITIONS

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.

Thyroxine (T4): the major hormone produced by the thyroid gland. T₄ gets converted to the active hormone T₃ in various tissues in the body.

Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.

Subclinical Hypothyroidism: a mild form of hypothyroidism where the only abnormal hormone level is an increased TSH. There is controversy as to whether this should be treated or not.