Diagnosis of Hypothyroidism

Diagnosis of hypothyroidism is easy using laboratory findings. If an individual is suspected of having hypothyroidism, lab investigations will clearly identify the condition. Problem of diagnosis arises in case of subclinical hypothyroidism, where patients are usually asymptomatic and do not seek any medical attention. It is detected during routine investigations for other medical conditions. Many experts recommend screening for hypothyroidism among suspected groups, such as elderly women and pregnant women.

How hypothyroidism is diagnosed?

The diagnosis of hypothyroidism is based on laboratory findings of TSH (thyroid stimulating hormone) and thyroid hormones (T3 and T4). In most cases measurement of TSH provide a picture of thyroid status. In case of hypothyroidism, TSH is high (due to production of excess TSH by hypothalamus, which stimulate thyroid gland to produce more T3 and T4). In case of hypothyroidism, TSH is low, which is because of less production of TSH by hypothalamus, due to excess T3 and T4 which give negative signal to hypothalamus.

Sometimes problem arises, when T3 and T4 are normal, but TSH is high (normally when TSH is high, T3 and T4 are low). In this type of cases measurement of free T3 and T4 can be helpful. This can be called case of subclinical hypothyroidism. This type of cases are also sometimes seen, during treatment of hypothyroidism (patient is on thyroxin).

For more precise finding, free levels of T3 and T4 are tested, which give a better picture of the problem. Because, it is the free T3 and T4 that are active hormones and responsible for clinical condition/response. For example a person may have normal total thyroid hormones (T3 and T4), but the free forms may be lower than normal, this person is most likely to have symptoms of hypothyroidism, despite having normal values for total thyroid hormones (T3 and T4). Similarly, a person with low level of total thyroid hormones may not have any symptoms of hypothyroidism, because his/her, free thyroid hormones (T3 and T4) may be normal. Hence, the person may not be considered to be case of hypothyroidism and does not need treatment with thyroxin.

Should screening done for hypothyroidism?

In many countries screening for thyroid function (hypothyroidism) is done using TSH level to high risk groups such as new born infants (diagnosis can help prevent developmental delays due to subnormal thyroid function), elderly women (during routine annual physical examination), pregnant women. It is subject of debate, whether to screen or not screen for hypothyroidism. If resources are available, at least high risk groups can be screened for hypothyroidism, which may ultimately prove beneficial to the society.

 

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