SCREENING FOR INFRACLINICAL HYPOTHYROIDIS M WITH THE TRH TEST AND ANTI-TPO ANTIBODY-ASSAY

The upper limit of normal TSH levels, determined with a second generat ion kit (RIA-Gnost TSH, Behring) was set at 2.8 mu U/ml. These TSH lev els define pituitary reactivity in euthyroid subjects. The upper limit for TSH 20 minutes after injection of TRH was set at 23 mu U/ml. The diagnosis of infraclinal hypothyroidism should be made in patients wit h a normal hormone level, normal baseline TSH and a positive response to TRH defined as a TSH above the upper limit 20 minutes after injecti on. A large percentage of these patients were positive for anti-TPO an tibodies, emphasizing the risk of developing patent hypothyroidism. Cl inicians should be aware of the need to lower the upper limit for base line TSH, often set a 4 or even 6 mu U/ml. A level of 2.8 to 4 mu U/ml is recommended as the upper limit. Within this interval, the TRH test should always be performed since 50 % of the TSH values obtained unde r in such patients are abnormal.