Subclinical hypothyroidism (SCH) is defined as a serum thyroid-stimulating hormone (TSH) level above the upper limit of normal despite normal levels of serum free thyroxine. Serum TSH has a log-linear relationship with circulating thyroid hormone levels (a 2-fold change in free thyroxine will produce a 100-fold change in TSH). Thus, serum TSH measurement is the necessary test for diagnosis of mild thyroid failure when the peripheral thyroid hormone levels are within normal laboratory range. The individual range for peripheral thyroid hormones is narrower than the population reference laboratory range; therefore, a slight reduction within the normal range will result in elevation of serum TSH above the normal range.

Thank you. However, that was not the question I asked. I am interested in who first used the term subclinical in connection with thyroid disease.

Hypogonadism, hypocortisolism and subclinical hypothyroidism: case report

M Henze - Reactions, 1713 - SpringeR

Dear Dr. Salem A Beshyah kindly see the following links:

Article Subclinical hypothyroidism: A historical view and shifting prevalence

Article History of disorders of thyroid dysfunction

Article Hypothyroidism and Thyroid Substitution: Historical Aspects

Thanks. It's better tan I did with the question.

Incidentally, I noticed Nooralhuda Alfatlawi's definition of S.H.

My definition is reduction of T3 from the patient's usual level, with elevation of Reverse T3, high enough to render T3/RrT3 < 20.0. This reduction of the ratio indicates failure to convert T4 into T3 and needs Rx with SLOW RELEASE triiodothyronine.

Note that for this calculation, TSH is of little value, but if it happens to be high, lowest effective dose of T4 needs to be added.

Note that Rx T4 makes the condition worse, due to preferential conversion of T4 to rT3.

Note also that the patient typically presents with hypothyroid symptoms.