067 - The diagnosis of thyroid disease; the question of the clinician and the answer of the laboratorian
Autor(s): R.M. Dorizzi, R. Castello
Issue: RIMeL - IJLaM, Vol. 3, N. 3-S1, 2007 (MAF Servizi srl ed.)
Page(s): 67-75
Thyroid diseases represent the most frequent endocrine disease especially in the women. It has been estimated that in Italy about 50% of population has thyroid nodules; 15% palpable goiter, 10% functional disorders and 5% symptomatic hypo- and hyperthyroidism. In the recent years guidelines about the different aspects of the management, in some cases consistent, but in others conflicting, have been proposed. According to the l’U.S. Preventive Services Task Force it is not yet possible to estimate the benefits and the damages of the screening of the asymptomatic adults. The document prepared by the Guidelines National Program (including the section devoted to the several and important drugs interferences) has a great practical interest and has been shortly summarized. There are at least two strategies for the laboratory diagnosis of thyroid disease; one proposed more than 20 years ago by Klee, based on TSH alone, ad that recently reproposed by the British Thyroid Association (BTA) based on both TSH and FT4. BTA recommends this approach when the pituitary- thyroid axis is damaged or is unstable. According to the Klee’s proposal, the subject is classified as euthyroid when the TSH concentration is within the reference limits and further tests are carried out only when TSH concentration exceeds the reference limits. Really, TSH is the most sensitive indicator of mild hypo- and hyperthyroidism since the correlation between TSH and FT4 is not linear; when FT4 concentration falls 50%, TSH concentration does not doubles but rises many times more. Our laboratory adopted a similar automatic algorithm in 2003; the access of the patient is unique and the collected sample is sufficient for carrying out all the needed (and sufficient) tests. The patient or the National Health System pay for the carried out tests needed for the specific patient and the report is not delayed. The pregnancy demands special care in thyroid function assessment because the fetus increases thyroxine requirements and the changes of the immune system increases the risk of autoimmune diseases and influence the history of autoimmune thyroid diseases. There are still problems in the assay of TSH and thyroglobulin (Tg) such as the great variation of the functional sensitivity of the commercial assays and the low homogeneity of the reference intervals. The assay of Tg, that has the single indication of the follow up of thyroidectomized patients, suffers from anti-Tg antibodies interferences. Also the most recent studies demonstrated that the problem is still unresolved.