Time of Day Does Matter For TSH
It sometimes feels like you are banging your head against a wall.
You believe something, you repeat it, and repeat it, and repeat it.................................
Then you start to have a moment of self-doubt. Surely, if that thing is true, the whole world would already have woken up and taken it into account? Perhaps I am wrong...
Eventually you see a paper, a real clinical research paper, which revives your belief. So you want to shout it from the rooftops. Again.
This is such a paper. 
The take-home message is:
If you want your TSH test to get you diagnosed hypothyroid, get the blood drawn in the morning, as early as possible.
In my view, now that TSH reference ranges are somewhat more sensible than they were, say, ten years ago, this variation through the day has increased in importance.
And, of course, the same basic argument applies when TSH is used to monitor treatment.
Endocr Res. 2013;38(1):24-31. doi: 10.3109/07435800.2012.710696. Epub 2012 Aug 2.
Clinical significance of TSH circadian variability in patients with hypothyroidism.
Sviridonova MA, Fadeyev VV, Sych YP, Melnichenko GA.
Source
Federal Endocrinological Research Centre, Moscow, Russia. maska119@rambler.ru
Abstract
OBJECTIVE:
To investigate the clinical significance of thyroid-stimulating hormone (TSH) circadian variability in patients with hypothyroidism.
DESIGN:
A total of 20 women with subclinical hypothyroidism and 22 patients taking L-thyroxine replacement therapy for hypothyroidism were enrolled in the study. Measurements of serum TSH levels were done twice a day from 08.00 to 09.00 a.m. and from 2.00 to 4.00 p.m.
RESULTS:
The morning median TSH value in the patients with subclinical hypothyroidism was 5.83 mU/L; in the afternoon, it was 3.79 mU/L. The range of TSH circadian variability reached the level of 73%. According to the current TSH reference interval, hypothyroidism was not diagnosed in about 50% of the cases in the afternoon. The morning median TSH value in the patients taking l-thyroxine was 3.27 mU/L; it decreased to the value of 2.18 mU/L in the afternoon. The range of TSH circadian variability reached the level of 64.7%. Further analysis demonstrated inadequate compensation of hypothyroidism, which was defined in 45.5% of the morning samples and in 9% of the afternoon samples (p < 0.05).
CONCLUSION:
The time of blood sampling has an important role in the interpretation of TSH levels. Moreover, the high TSH circadian variability should be considered in discussions about the narrowing of its reference range.
PMID: 22857384 [PubMed - in process]
www.ncbi.nlm.nih.gov/pubmed...
Rod
Alarm clock - maybe a bit too early to find someone to draw your blood?