Endocrine Abstracts (2009) 20 P145

Assessment of biochemical parameters during Levothyroxine replacement therapy in hypothyroid patients

Romana Mijovic1, Milica Medic-Stojanoska2, Nikola Curic1, Stanislava Tonic1, Branka Kovacev-Zavisic2 & Ljiljana Djilas-Todorovic2


1Center for Laboratory Medicine, Clinical Center of Vojvodina, Novi Sad, Serbia; 2Clinic for Endocrinology, Diabetes and Metabolic Disease, Clinical Center of Vojvodina, Novi Sad, Serbia.


Aim of this study was to evaluate biochemical parameters of thyroid gland function, used in evaluation of levothyroxine (L-T4) dose titration during a long time period in hypothyroid patients.

Patients and methods: About 32 hypothyroid women were included in our study. All patients were euthyroid for a long time, treated with levothyroxine replacement therapy, taking an individually titrated daily dosage (50–100 μg). Blood samples were taken from all the patients before therapy (on empty stomach), and two hours after therapy administration. In both blood samples, the following parameters were estimated: TT3, TT4, fT3, fT4 i TSH. Those parameters were measured at once by immunometric assays on ARCHITECT i2000SR. All data were processed by standard statistical analysis.

Results: There is statistical significant increment (P<0.05) of fT4 (X=14.9 pmol/l; S.D.=1.9) and TT4 (X=118 nmol/l; S.D.=21.2) values after levothyroxine administration regarding the values measured before therapy (fT4:X=13.6 pmol/l; S.D.=1.7; TT4: X=107.5 nmol/l; S.D.=19.2). There is no statistical difference between values of fT3 and TT3 before and after administration of replacement therapy (P>0.05). After therapy administration, there was an estimated decrement of TSH values (X=2.07 mIU/l; S.D.=1.45) regarding the values of TSH before the therapy (X=2.76 mIU/l; S.D.=1.98), but with no statistical difference (P=0.06) due to high S.D.

Conclusion: Time interval between levothyroxine administration and blood sampling for fT4, TT4 and TSH measurements should be accounted for order to evaluate the apllicated levothyroxine dose. Due to these results, it is recommended that blood samples should be collected before L-T4 therapy administration in clinically euthyroid and overtly hypothyroid patients, but when there is a suspicion of overdose with L-T4, blood samples should be taken at least two hours after received therapy.

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