 The reference range for serum TSH is wide currently 0.34-4.8 mUL at PathCentre. The distribution of serum TSH concentrations in the population is skewed, with the mean and median in the lower reference range at approximately 1.0 mUL. This has led some to argue that a serum TSH in the lower reference range should be the usual therapeutic target. Anecdotal evidence suggests that some thyroxine-treated patients do feel better if the thyroxine dose is adjusted so that serum TSH is in the lower reference range rather than the upper reference range. The National Academy for Clinical Biochemistry of the United States now recommends, that for thyroxine-treated patients, that serum TSH should be less than 2.0 mUL. There is, however, no evidence from properly conducted studies that aiming for a serum TSH concentration in the lower reference range improves symptoms of hypothyroidism or general wellbeing, and this proposal has not been generally adopted. 