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A single TSH (Thyroid Stimulating Hormone) blood test is commonly used to help diagnose thyroid problems, however my understanding is that the TSH tends to vary substantially over the course of a day, based on time of day (eg TSH is highest at about 5am, from memory).
Is there data and/or a chart available that illustrates typical variation over the course of a day for people with a healthy thyroid? How about for people with thyroid problems?
TSH has a quite important circadian rhythm.
Most of the original research on it is not freely accessible, as open access wasn't really a thing when these studies were done, in the 80s, but this one is freely available: Physiological variations in thyroid hormones: physiological and pathophysiological considerations. There is a section on circadian and seasonal rhythm and a table with some values. Quoting from the paper:
There is a clear circadian variation in circulating TSH concentrations in animals and in humans. TSH concentrations are low during the daytime, increase in the evening, and peak shortly before sleep. Amounts decline slowly during sleep. Table 3 summarizes studies of mean, nadir, and peak serum
They also mention that the nocturnal TSH secretion is weakened in people with hyperthyroidism.
A chart is available in figure 2 of the paper Modulation of Endocrine Function by Sleep-Wake Homeostasis and Circadian Rhythmicity
Hyperthyroidism
Significance of latent hyperthyroidism is another study from the 80s on this. They found a significant circadian rhythm in normal (euthyroid) patients, but a suppressed rhythm in subjects with hyperthyroidism, the suppression getting stronger the worse the hyperthyroidism is:
The circadian rhythm in latent hyperthyroidism is distinctly suppressed and in overt hyperthyroidism totally. Whereas in latent hyperthyroidism pulsatile secretion is extant, in overt hyperthyroidism the TSH pulses are absent.
Hypothyroidism
The same is basically observed in hypothyroidism, see, for example Diurnal thyrotropin secretion in short-term profound primary hypothyroidism: does it ever persist?
In conclusion, diurnal rhythmicity in serum TSH levels was abolished in a uniform cohort of patients with short-term severe primary hypothyroidism.
or Circadian changes in pulsatile TSH release in primary hypothyroidism.
The nocturnal TSH surge was absent in six out of nine patients with overt primary hypothyroidism.
The circadian rhythm is weaker, different, or even absent.
While I have always had doctors recommend having TSH done in the morning, without eating beforehand, this doesn't seem to be a general suggestion. However, it's at least desirable to always have them done at the same time of day, to make values comparable:
TSH has a circadian rhythm (24 hour cycle) and levels peak between midnight and 6am. T3 has a similar circadian rhythm. It is therefore a good idea to have your thyroid tests done at the same time of day each time as your levels may differ at different times of the day.
Word explanation:
TSH concentration is subject to both circadian variation (i.e. a rhythm with a period of one day) and ultradian variation (i.e. faster oscillations).
This fact is illustrated by the following figure:
This illustration was generated by computer simulations. Model 4 integrates long and ultra-short feedback control of TSH release. The pattern generated by this fourth model is identical to that of natural time series, as proved by two methods to calculate fractal dimensions [Hoermann R, Midgley JE, Larisch R, Dietrich JW. Homeostatic Control of the Thyroid-Pituitary Axis: Perspectives for Diagnosis and Treatment. Front Endocrinol (Lausanne). 2015 Nov 20;6:177. doi: 10.3389/fendo.2015.00177. PMID 26635726; PMCID PMC4653296].
The following figure illustrates TSH pulsatility over three weeks in the evolution of non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumours, uremia and starvation (TACITUS).
This time series was again created by numeric simulation, but it is identical to observations of real patients [Dietrich JW, Landgrafe G, Fotiadou EH. TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis. J Thyroid Res. 2012;2012:351864. doi: 10.1155/2012/351864. Epub 2012 Dec 30. PMID 23365787; PMCID PMC3544290.].
All time series were created with SimThyr 3.
