[The interpretation of the thyroid stimulating hormone (TSH) assay].
Current immunometric TSH assays guarantee a functional sensitivity of at least 0.10 mU/l. The 95% confidence interval of TSH reference values is 0.45-4.12 mU/l; it becomes slightly broader above the age of 60 years (0.4-5.9 mU/l for 70-79 years). Interference by heterophilic antibodies in the TSH assay may give rise to spuriously elevated TSH values. The TSH assay is a very accurate diagnostic test for screening thyroid function. A normal TSH indicates euthyroidism with an accuracy of > 99%; only the rare patient with central hypothyroidism may be overlooked, but the history usually provides sufficient clues to suspect hypothalamic or pituitary disease. In case of an abnormal TSH value, a FT4 assay should be done. Each of the six possible outcomes (decreased or increased TSH combined with a decreased, normal or increased FT4 value) points to a specific diagnosis with an accuracy of over 90%. In the follow-up of treatment of thyroid function disorders, TSH target values are slightly different from the normal reference values. In primary hypothyroidism one aims at TSH values between 0.25 and 2.0 mU/l, but should avoid TSH values < or = 0.10 mU/l. In differentiated thyroid cancer, following complete thyroid ablation the target value is < or = 0.10 mU/l. A decreased TSH value in the course of treatment for Graves' hyperthyroidism does not necessarily indicate thyrotoxicosis, but may reflect persisting levels of TSH receptor stimulating antibodies.
Wiersinga
W M
WM
Academisch Medisch Centrum/Universiteit van Amsterdam, afd. Endocrinologie en Metabolisme, Meibergdreef 9, 1105 AZ Amsterdam. w.m.wiersinga@amc.uva.nl
D000367:Age Factors; D000368:Aged; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000175:diagnosis; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis; D008297:Male; D012016:Reference Values; D012680:Sensitivity and Specificity; D013959:Thyroid Diseases / Q000097:blood / Q000175:diagnosis*; D013960:Thyroid Function Tests / Q000379:methods*; D013972:Thyrotropin / Q000032:analysis* / Q000097:blood; D013974:Thyroxine / Q000097:blood
D013972:Thyrotropin; D013974:Thyroxine