Laboratory Tests
Measurements [B]
Standard laboratory measures have been established for thyroid disease.
T3 and T4 [C]
This measure is a defining feature of the diseases. T3 and T4 levels are elevated in hyperthyroid and reduced in hypothyroidism.
Iodine Uptake
Radioactive iodine is utilized to allow monitoring of uptake, by measurement of radioactive emissions at the neck in the region of the thyroid gland. In general, iodine uptake is increased in hyperthyroid cases, due in part to the larger amount of thyroid tissue and the higher production of the iodine-based T3 and T4, and iodine uptake is reduced in hypothyroidism. Clinical values for iodine uptake usually keep pace with those for T3 and T4 production.
BMR
Basal metabolic rate is raised in hyperthyroid cases and lowered in hypothyroid cases. Because metabolic rate is influenced by T3 and T4 levels, the BMR measurement closely follows the T3 and T4 measures.
TSH
Thyroid-stimulating hormone is released from the pituitary in a feedback loop with T3/T4 levels in normal individuals. TSH levels are usually reduced in hyperthyroidism and elevated in hypothyroidism.
Laboratory Tests [B]
TSH Assay [C]
The best test for thyroid function to rule out thyroid pathology is TSH (thyroid stimulating hormone). TSH is a highly sensitive assay. When TSH is high, the patient will have primary hypothyroidism. Low TSH levels indicate primary hyperthyroidism. If TSH is normal, it excludes any conventional primary thyroid pathology.
However, this does not take into account secondary thyroidism from the hypothalamus, or pituitary gland, subclinical hypothyroidism, Wilson’s Temperature Syndrome, or thyroid resistance. These conditions will usually have other symptoms that would suggest the need for further diagnostic work or clinical history.
When treating hypothyroid patients with exogenous hormones, TSH levels should be within normal range, However, one should not adjust dosage based on merely TSH values because it is much more important to adjust thyroid hormone supplementation based on clinical results. It should be low when thyroid hormone therapy is used to suppress thyroid function as in benign nodules, thyroid malignancy, or Wilson’s Temperature Syndrome.
Free Thyroid Hormone Assay [C]
This the best test to order. Free T3 and T4 are unbound and bioactive. Free thyroid hormone levels are abnormal in thyroid dysfunction. If total thyroid levels are abnormal, it is possible that the thyroid may be functioning fine, due to the fact that most thyroid hormones are bound to proteins: 99% of T4 and 98% of T3 are bound to the carrier proteins thyroid binding globulin (TBG), albumin, and pre-albumin. Factors that will increase binding capacity are pregnancy, estrogen, and increased levels of conjugated TBGs. Factors that decrease binding are androgens and congenital TBG deficiency.
Blood Tests [C]
Thyroid stimulating immunoglobulin blood test is used to diagnose Grave’s disease. Anti-thyroid peroxidase and antithyroglobulin antibodies are used to diagnose Hashimoto’s thyroiditis.4
Calcitonin [C]
Calcitonin levels are measured to diagnose medullary carcinoma of the thyroid. This is a very rare condition and need not be ordered on a routine thyroid test.
Thyroid Scan [C]
A thyroid scan is good to rule out thyroid nodules. Thyroid scan presents diffuse trace uptake in Grave’s disease and non-diffuse in toxic multinodular goiter. Discrete uptake in a single area presents as solitary toxic adenoma.
RAI [C]
The difference between a thyroid scan and radioactive iodine uptake diagnostic testing is that RAI gives a quantitative status of thyroid gland, while the scan portrays a two dimensional representation used to differentiate between isolated nodules and uniform distribution of the pathology. Radioactive iodine isotopes are used to distinguish causes of hyperthyroidism.
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Selected Clinical Studies and Literature Reviews
For a full discussion of thyroid hormone metabolism and naturopathic treatments of thyroid disorders, see Gregory S. Kelly, “Peripheral Metabolism of Thyroid Hormones: A Review,” in Selected Clinical Studies and Literature Reviews, pp. xx-xx.
