Thyroid hormone 24-hr. urine


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    The thyroid produces two hormones, tyroxine (also called T4) and tri-iodothyronine (also called T3). More T4 is produced and circulated than T3, but the T3 is more active than T4. Although T4 also has its own activity, it has to be considered as a pro-hormone of the active (er) T3, which is formed from this. The thyroid hormones are important for (basic) body metabolism. They stimulate the basic consumption of oxygen and the metabolism and lead to the production of heat.

    When there is a suspicion of hypo- or hyperthyroidism (a too slow and too strong thyroid gland), the levels of TSH, T3 and / or T4 in the blood are usually measured. In practice, however, it turned out that the level of T3 (and T4) in 24-hour urine showed a better correlation with the symptoms, particularly in an early stage of hypothyroidism. When symptoms are present that may indicate a (mild) hypothyroidism often (still) normal blood values are found, while the values in 24-hour urine (already) deviate and confirm the suspicion of (mild) hypothyroidism. The test is therefore particularly suitable for those cases in which symptoms of hypothyroidism are not (yet) confirmed by the usual blood tests.

    Several scientists have expressed the suspicion that a not insignificant percentage of the population suffers from (subclinical) hypothyroidism, that this disorder occurs much more frequently than is thought and that the percentage of people who suffer from this increases.

    Some symptoms that are often seen in hypothyroidism are:

    Coldness (cold extremities)
    Fatigue (especially in the morning)
    Dry skin
    Slow peristalsis / Constipation (constipation)

    See also The Official Web Site of the International Hormone Society.

    More information

    The thyroid is incited to the production of T4 and T3 by Thyroid-Stimulating Hormone. (TSH) produced by the pituitary gland. The production of this substance is stimulated again by Thyrotropin-Releasing Hormone (TRH) produced by the hypothalamus. T3 and to a lesser extent also T4 inhibit the formation of both TSH and TRH via a negative feedback.

    Accordingly, the formation of TSH is stimulated by cold and inhibited by heat. Certain stress situations also inhibit TSH.

    Thyroid function can be negatively affected (reduced) by low adrenal function, malnutrition (eg iodine and tyrosine) and aging.

    The conversion of T4 to T3 can be negatively affected by, inter alia, aging, malnutrition (such as selenium, zinc and copper deficiency), low adrenal function, beta-blockers and the contraceptive pill.

    Except in T3, T4 can be converted into rT3 (3,3,5 tri-iodo thyronine or reverse T3). This hormone is not biologically active and reduces the activity of T3. Promoting one over another conversion offers the body an additional possibility to regulate body metabolism, such as in hyper- or hypothyroidism.5 In line with the expectation, a reduced T3 / RT3 ratio has been found in hyperthyroidism, and an increase in hypothyroidism.

    Non-thyroid related disorders can also affect (decrease) the T3 / rT3 ratio, which may cause signs of hypothyroidism. A reduced T3 / rT3 ratio was found among other things in fasting, stress due to (heavy) operations, liver cirrhosis and insulin-dependent diabetes.


    It is useful to test for T3 and T4 in 24-hour urine when there are symptoms of hypothyroidism, but the results of the usual blood tests are (still) normal. The test can also be used to check the effect of a used therapy.

    Symptoms that may indicate hypothyroidism are:


    Coldness (cold extremities)
    Fatigue (especially in the morning)
    Low basal body temperature (<36.7 C)
    Mix-Edema (fluid retention)
    Decreased appetite
    Dry skin
    Brittle nails
    Dry, stiff, slowly growing hair
    Muscle and joint pain
    Deafness and tinnitus
    Little resistance to infections (mainly of the airways)
    To speak hoarseness / sluggishness
    Extended Achilles tendon reflex

    Mental / nerves

    Carpal tunnel syndrome
    Reduced memory