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Thyroid function tests in patients with acute and resolved hepatitis B virus infection.

Serum thyroid hormones and thyroid hormone binding were sequentially measured in 20 patients with acute hepatitis B infection. Criteria to select patients consisted of a positive test for hepatitis B surface antigen, aspartate aminotransferase (AsAT) concentration greater than 400 U/L during the acute illness, and available serum specimens after recovery. The mean serum thyroxine (T4) concentration (+/- SE) was 12.5 +/- 0.6 microgram/dL during acute infection and 7.4 +/- 0.3 microgram/dL after recovery (p less than 0.001), whereas mean free T4 index values did not significantly differ. The mean serum thyroxine-binding globulin (TBG) concentration was significantly increased (p less than 0.001) during acute illness and accounted for the reversible of serum and the increased serum T4 concentrations. The rise in serum TBG correlated with the rise in AsAT during the acute illness (p less than 0.04) suggesting nonspecific release of these proteins from injured hepatocytes. The mean free triiodothyronine (T3) index was decreased during acute hepatitis (p less than 0.001) and returned to normal after recovery, indicating that acute hepatitis B infection, like other nonthyroidal illnesses, is associated with decreased T4 to T3 conversion in peripheral tissues.

Acute Disease↗

Thyroid function testing evaluated on three immunoassay systems.

Total thyroxine (TT4), tracer uptake, thyroid-stimulating hormone (TSH), and free T4 (FT4) testing was examined in the ACS 180, Abbott IMx, and Stratus II systems. TSH sensitivity studies demonstrated that the ACS and IMx are second-generation assays; the Stratus showed between first- and second-generation performance. Except for one control below the detection limit, TSH imprecision was 3-10%. TSH accuracy was adequate for all systems. TT4 imprecision was 4-7%, except for the lowest control with the Stratus (18%). TT4 method agreement showed bias of about 20% between the systems. TT4 accuracy was compromised at the low end for the Stratus II, but was satisfactory otherwise. FT4 imprecision was 20% for the Stratus, < 5% for the IMx and 6% for the ACS. Uptake assays showed imprecision of 5-10%. The laboratory diagnosis indicated by each system's FT4 and calculated FT4 Index results were compared to determine diagnostic accuracy. In routine specimens, different clinical classifications were observed for 25% of specimens with the ACS, 19% with the Stratus, and 7% with the IMx; in the altered protein group, the Stratus showed 9% discordant results, the ACS showed 3%, and the IMx 0%. Of the three systems examined here, the Abbott IMx system showed the best overall performance.

Humans↗

Changes in thyroid function tests induced by 2 month carbamazepine treatment in L-thyroxine-substituted hypothyroid children.

In five L-thyroxine-substituted hypothyroid children with partial epilepsy serum total thyroxine (T4) and free T4 (FT4) significantly (P less than 0.01) decreased following 2 months of carbamazepine (CBZ) administration (20 mg/kg per BW per day) from mean (+/- SD) values of 12.7 +/- 1.1 micrograms/dl and 15.5 +/- 1.8 pg/ml to mean values of 7.5 +/- 2.3 and 10.1 +/- 1.7, respectively. In all but one patient important changes in both serum total and free triiodothyronine (T3, FT3) were not observed; consequently T3:T4 and FT3:FT4 ratios significantly (P less than 0.05) increased in the whole series. Three subjects had post-treatment serum TSH that rose to hypothyroid levels parallel to a T4 decrease. The negligible thyroid hormone secretion and the unmodified T3-uptake (T3U) or T4-binding globulin (TBG) exclude direct effects of CBZ on thyroid gland and on carrier serum proteins, respectively. The findings observed, instead, might be due to accelerated T4 metabolic clearance together with augmented T4 to T3 conversion rate, as previously demonstrated for diphenylhydantoin. The sharp reduction in T4 and FT3 concentrations is the peripheral display of this event, which is associated with a decompensation of the metabolic status, as indicated by serum TSH enhancement. In all cases a supplement of L-thyroxine by itself was able to restore euthyroid TSH serum concentrations, suggesting that hypothyroidism in patients with partial epilepsy to whom CBZ had been administered requires a higher L-T4 substitutive regimen.

Carbamazepine↗