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Diurnal TSH Variations in Hypothyroidism

Second University Clinic of Internal Medicine Kommunehospitalet, 8000 Aarhits C, Denmark

There is a circadian variation in serum TSH in euthyroid subjects. A similar diurnal variation has not been demonstrated in patients with hypothyroidism. In the present study the 24-hour pattern of serum TSH was investigated in eight patients with hypothyroidism of varying seventy and in five hypothyroid patients treated with thyroxine (T₄). There was a circadian variation in serum TSH in patients with hypothyroidism of moderate degree, and in patients treated for severe hypothyroidism with thyroxine. The pattern was similarto that found in normal subjects, i.e., low TSH levels in the daytime and higher levels at night. In severely hypothyroid patients, no diurnal variation in serum TSH was observed.

A practical consequence is that blood samples for TSH measurements in patients with moderately elevated TSH levels are best taken after 1100 h, when the low day levels are reached.

Received December 9, 1975.

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