Time of day makes a difference in thyroid testing, by Jacob Schor ND, August 14, 2012
TSH levels follow a circacian rhythm:
peak levels at 2-4am, lowest levels at 4-8pm
Extent of fluctuations greater than previously imagined
Afternoon samples lead to under diagnosis of hypothyroidism
(Not even counting the dispute about what ranges to be used.
Conventional: 0.5-5.0 mU/L.0)
Best time to collect: first thing in the morning
CV dz much more with TSH levels under 2.5.
REF: Duntas LH, Biondi B. New insights into subclinical hypothyroidism and cardiovascular risk. Semin Thromb Hemost. 2011 Feb;37(1):27-34. Epub 2011 Jan 19.
Federal Endocrinological Research Centre in Moscow
N = 20 women with subclinical hypothyroidism
Median morning TSH value for women with subclinical hypothyroidism was 5.83 mU/L.
Afternoon median was 3.79 mU/L.
REF: Sviridonova MA, Fadeyev VV, Sych YP, Melnichenko GA. Clinical Significance of TSH Circadian Variability in Patients with Hypothyroidism. Endocr Res. 2012 Aug 2.