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Dr. Q’s Questions for March

1. Why are TSH results of samples taken a few weeks apart seemingly discrepant? 

TSH exhibits not only pulsatile secretion with an amplitude of about 1 mU/L, but a modest circadian pattern with a nadir in the mid-afternoon. TSH peaks daily around 1400 with a marked decline from about 0700 to 1000, the period most patients visit our collection sites (see Fig. 1 below). This change may be substantial – up to 3 mU/L. Analytical factors add only a modest level of scatter, typically less than 1 mU/L.

2.How do you interpret and act upon a TSH result consistent with subclinical hypothyroidism?

An excellent on-line Communiqué was recently published by the Mayo Clinic and can be found at: www.mayomedicallaboratories.com. 

Dr. Jan Palaty, Clinical Biochemist

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