engleski

TT4 vs. FT4 in laboratory practice

Thyroid function tests are among the most common requirements in the laboratory. According to the guidelines, thyrotropin (TSH) is recommended as a first test for thyroid function. If the TSH is outside the RI it’s recommended to make FT4. FT4 is the biologically active fraction of the hormone that doesn’t depend on the concentration of binding proteins, and has a better detection of the discriminative power of the hypoor hyperthyroidism in relation to TT4. However, severe nonthyroid diseases, the treatment of heparin and some medications, and fasting may increase FT4 with no indications of increased secretion of T4. The aim of this study was to measure the concentration of TT4 in patients with increased FT4 while normal TSH, and in patients with normal TSH and FT4. The concentrations of TSH, FT4 and TT4 were measured in serum samples (n = 78) by chemiluminescent microparticle immunoassay (CMIA) on UniCel DxL600 (Beckman Coulter Inc., Brea, USA). The results were processed by MedCalc (MedCalc Software, Mariakerke, Belgium). The analysis shows that only 5 patients (11%) of the total 44 have elevated TT4 with elevated FT4 and normal TSH. Correlation coefficient between TT4 and FT4 for these subjects was 0.68. Others have TT4 within the RI, in accordance with TSH and clinical data. The results showed that certain factors can influence the concentration of FT4 and so result in nonconformance with TSH values %u200B%u200Band the clinical data. In order to obtain more accurate indication of the thyroid function in these patients is needed to measure and TT4.

Thyroid, TT4, fT4

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