TSH Levels in Treated Versus Untreated People: Medical Journals

Purpose of this compilation

To show that TSH and other thyroid lab tests may have different results in people on thyroid hormone supplementation than in people without thyroid dysfunction.

See also the links in the right column as well as in our T3 References and Desiccated Thyroid References sections.

A. TSH levels in the general population
B. TSH levels for people on thyroid supplementation

A. TSH levels in the general population

1. "Serum TSH, T4, and Thyroid Antibodies in the United States Population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III)" (US, 2002)

NHANES III measured serum TSH, total serum T4, antithyroperoxidase (TPOAb), and antithyroglobulin (TgAb) antibodies from a sample of 17,353 people aged ≥12 yr representing the geographic and ethnic distribution of the U.S. population....

...A reference population of 13,344 people was selected from the disease-free population....

...Using the reference population, geometric mean TSH was 1.40 ± 0.02 mIU/liter.

2. "Prevalence of thyroid disease, thyroid dysfunction and thyroid peroxidase antibodies in a large, unselected population. The Health Study of Nord-Trondelag (HUNT)." (Norway, 2000)

In individuals without a history of thyroid disease the median, 2.5 and 97.5 percentiles for TSH (mU/l) were 1.80 and 0.49-5.70 for females and 1.50 and 0.56-4.60 for males....When excluding individuals with positive thyroid peroxidase antibodies (TPOAb) (>200U/ml), the 97.5 percentiles dropped to 3.60 mU/l and 3.40 mU/l respectively....In females the lowest percentage (7.9%) of positive TPOAb was seen with TSH 0.2-1.9mU/l and increased both with lower and higher levels of TSH.

B. TSH levels for people on thyroid supplementation

1. "NACB: Laboratory Support for the Diagnosis and Monitoring of Thyroid Disease: Published Guidelines" (US, 2002)

Despite the clinical sensitivity of TSH, a TSH-centered strategy has inherently two primary limitations. First, it assumes that hypothalamic-pituitary function is intact and normal. Second, it assumes that the [patient's] thyroid status is stable, i.e. the patient has had no recent therapy for hypo-or hyperthyroidism....If either of these criteria is not met, serum TSH results can be diagnostically misleading.

2. "TSH as an index of L-thyroxine replacement and suppression therapy" (Ireland, 1992)

It is theoretically possible that patients receiving exogenous L-thyroxine for primary hypothyroidism should have suppressed TSH levels if physiological needs are constantly met. To examine this possibility free thyroxine, FT4 and TSH were measured in 90 clinically euthyroid patients receiving treatment with L-thyroxine for primary hypothyroidism....Normal TSH levels were associated with normal FT4 levels in 79.5% of patients, elevated FT4 levels in 13.6% and low FT4 in 6.8%. Suppressed TSH levels were associated with elevated FT4 levels in 37.5% of patients and normal FT4 levels in 62.5%. When FT4 levels were normal, however, TSH levels were normal in only 51.5% and abnormal in 48.5%.

3. "Are biochemical tests of thyroid function of any value in monitoring patients receiving thyroxine replacement?" (UK, 1986)

Our data indicate that the reference ranges for serum total thyroxine, analogue free thyroxine, and thyroid stimulating hormone [TSH] in patients receiving thyroxine replacement are different from conventional references ranges. It is clear from table IV, however, that serum thyroid hormone and thyroid stimulating hormone concentrations cannot be used with any degree of confidence to classify patients as receiving satisfactory, insufficient, or excessive amounts of thyroxine replacement. [p.810]

Our findings emphasise the need for laboratories to make their users aware that the reference ranges for serum thyroxine, free thyroxine, and thyroid stimulating hormone concentrations in patients receiving thyroxine replacement are considerably different from the conventional ranges; they should also point out the limitations of these ranges. This is especially important for general practitioners and non-specialists, who generally rely on the biochemical findings more than specialist endocrinologists do in managing these patients. [p. 810]