Test Overview of Thyroid Panel

In order to fully diagnose thyroid disorders, the following labs are required. Note that many conventional medical practitioners use TSH as a screening tool, and run no further tests if TSH appears to be within normal limits. Dr. Weyrich prefers to run additional tests in any case where the symptom presentation suggests hypothyroidism, particularly if the axillary basal body temperature is below 97.8 degrees F or other symptoms of hypothyroidism present.

Sample Collection for Thyroid Panel

Practitioners differ on whether a person being treated for a thyroid condition should take their thyroid medication the morning before the test. Dr. Weyrich generally is interested in the hormone status as corrected by the supplemental thyroid hormone, and has his patients continue with their thyroid medication according to their regular schedule. Dr. Starr prefers to have his patients defer their morning dose until after the blood draw [Starr2005, pg 168].

Your doctor or lab may have different instructions that supersede the above.

Labs Performing Thyroid Panel Test

Test Name Name of LabLab Code Estimated Cost Processing Time Comments
TSH+TT4+TT3+rT3 Lab Express   $201   Dr. Weyrich's standard workup
Any Lab Test Now   $225  
SonoraQuest   $449  

Test Name Name of LabLab Code Estimated Cost Processing Time Comments
TSH SonoraQuest 8055 $57   Always run
LabCorp 4259    
TT4 SonoraQuest 8045 $36   Always run
LabCorp 1149    
TT3 SonoraQuest 8093 $122   Run if hypothyroid signs
LabCorp 2188    
rT3 SonoraQuest 8127 $235   Run if hypothyroid signs
LabCorp 2212    
fT4 SonoraQuest 9731     Run if hypothyroid signs
fT3 SonoraQuest 15739
(tracer dialysis)
    Run if hypothyroid signs
Thyroglobulin Antibodies SonoraQuest 9150     Run if Hashimoto's Thyroiditis is suspected.
70% sensitivity [Pagana2002, pg 103].
Microsomal Thyroid Peroxidase Antibodies SonoraQuest 9145     Run if Hashimoto's Thyroiditis is suspected.
95% sensitivity [Pagana2002, pg 103].

Costs cited are subject to change and may be reduced by insurance or cash discounts and increased by sample collection fees.

Theory of Thyroid Panel

Thyroid hormones regulate the energy metabolism of the body, acting much as a governor on a car or a thermostat. When the body is too hot or energy reserves are low, thyroid hormone is reduced. Conversely, when the body is too cold and energy reserves are high, thyroid hormone is increased.

Three main endocrine glands are involved in regulating thyroid hormone in the body: The hypothalamus and pituitary gland (in the brain) and the thyroid gland (in the throat).

The main hormones involved in the thyroid system are:

  • TRH (Thyroid Releasing Hormone) - produced by the hypothalmus.
  • TSH (Thyroid Stimulating Hormone) - produced by the pituitary gland.
  • T4 (Thyroxine, tetraiodothyronine) - produced by the thyroid gland. Increases oxygen availability in all tissues [Friedman2005, pg 93].
  • T3 (triiodothyronine) - made from T4, primarily in the liver and kidneys. Most active thyroid hormone; increases oxygen availability in all tissues and interacts with the mitochondria to increase energy production and thus regulate metabolic rate [Friedman2005, pg 93; Starr2005].

The three endocrine glands work together in a system of negative feedback, constantly monitoring and adjusting the status of the body:

  • Low free T4 levels in the blood prompts the hypothalamus to produce TRH.
  • TRH prompts the anterior pituitary gland to produce TSH.
  • TSH prompts the thyroid gland to release T4, which is produced by the thyroid gland.
  • T4 is converted to T3 in the liver and kidneys.
  • T3 is then disseminated in the blood throughout the body.
  • If T4 or T3 levels rise too high, a negative feedback loop to the hypothalamus reduces TRH production to maintain homeostasis.

One author suggests that the peripheral cells have some signaling mechanism back to the hypothalamus to indicate a need for more circulating thyroid hormone, but does not make clear the nature of this signaling mechanism [Starr2005, pg 67]. Most authors consider free T3 or T4 in the blood to be the primary signaling mechanism back to the hypothalmus.

TSH (Thyroid Stimulating Hormone)

When TSH is within the normal range, conventional medicine considers that the upper control centers in the brain hypothalamus and pituitary) have established homeostasis.

However, researchers have found that the symptom picture does not always correlate with TSH levels [Zulewski1997]. Practitioners of functional medicine note that in cases of periperal resistance to T4, normal levels of TSH and T4 may be insufficient to eliminate the signs and symptoms of hypothyroidism. In this case, supplementation with desiccated thyroid or custom-formulated T4/T3 blend may be necessary to attain remission of symptoms, even though TSH may be driven to subnormal levels (less than 0.01) that most allopathic doctors consider indicative of hyperthyroidism [Starr2005, pg 63].

TT4 (Total T4)

TT3 (Total T3)

This is the most biologically active thyroid hormone. Low levels when compared with TT4 indicate poor conversion of T4 into T3 by the peripheral tissues.

rT3 (Reverse T3)

This is an inactive isomer of T3 that may be elevated when T3 is low. Elevated rT3 may indicate a selenium deficiency or caloric restriction.

fT4 (Free T4)

This is the fraction of total T4 that is not bound to blood proteins and hence represents the amount of T4 actually available to the tissues. Free T4 should be within the upper limit of normal [Starr2005, pg 168].

fT3 (Free T3)

This is the fraction of total T3 that is not bound to blood proteins and hence represents the amount of T3 actually available to the tissues. Free T3 may be elevated if thyroid medications are taken in the morning before the blood draw, otherwise should be within the upper limit of normal [Starr2005, pg 168].

24 hour Urine T3

Another approach that has been discussed in the literature is an assay of T3 in 24-hour sample of urine. While this test is reported to accurately correlate with symptoms of hypothyroidism, the test is not widely used (yet) [Starr2005, pg 71; Hertoghe2001].

References regarding Thyroid Panel

[Friedman2005] Michael Friedman. Fundamentals of Naturopathic Endocrinology Toronto: Canadian College of Naturopathic Medicine (CCNM) Press (2005).

[Hertoghe2001] J. Hertoghe et al. Thyroid insufficiency. Is thyroxine the only valuable drug? Journal of Nutritional & Environmental Medicine 11:159-166 (2001). Cited by [Starr2005, pg 176].

[Pagana2002] Pagana Kathleen Deska & Pagana Timothy J. Mosby's Manual of Diagnostic and Laboratory Tests, Second Edition. St. Louis: Mosby (2002).

[Starr2005] Mark Starr. Hypothyroidism Type 2: The Epidemic. Columbia, MO: Mark Starr Trust (2005).

[Zulewski1997] H. Zulewski et al. Estimation of tissue hypothyroidism by a new clinical score: Evaluation of patients with various grades of hypothyroidism and controls. Journal of Clinical Endocrinology and Metabolism 82(3):771-776 (1997). Cited by [Starr2005, pg 70].

Unless specifically noted above, references used in the construction of this web page include the following:

[FDM] Lecture notes from Functional Medicine University.

[SCNM] Lecture notes from Southwest College of Naturopathic Medicine.

[UT] Lecture notes from the University of Tennessee graduate programs in Chemistry, Microbiology, and Biochemistry.