Mean FT4 Values Research Articles

Differences in the clinical picture at the onset of diagnosis of severe autoimmune hypothyroidism in children depending on the time of diagnosis: before or during the SARS-CoV-2 pandemic.

There are few data about effects of COVID-19 on thyroid disease presentation in children, due to difficulties in healthcare services access. To assess the differences in hypothyroidism presentation before and during the COVID-19 pandemic. All paediatric patients with autoimmune hypothyroidism (AIT) diagnosed from January 2017 to December 2022 were analysed. A total of 150 subjects were enrolled (94 in before and 56 during the pandemic period). Severe AIT was detected in 7.4% before and 12.5% during the pandemic. Age at the onset in the pre-pandemic period was lower ( p = 0.04). Diagnosis delay (time elapsed from onset of symptoms and diagnosis) was significantly different between the before and during the pandemic groups ( p = 0.02). In the pre-pandemic period the TSH value was 447.7 ±59.1, and it was 713.7 ±104.4 mUI/l during the pandemic ( p = 0.04), whereas mean fT4 values were 2.66 ±0.34 and 0.58 ±0.08 ng/l, respectively ( p = 0.0002). Significantly greater thyroid volume and bone age delay SDS were observed during the pandemic ( p = 0.04). Neurological symptoms were mostly observed during the pandemic, especially slow speech and impaired school performance. A higher rate of severe AIT was observed during the pandemic period, mostly related to difficulties in access to healthcare services. The diagnosis delay led to a more severe biochemical thyroid hormone profile, goitre, and more frequent presence of bone age delay and neurological symptoms at the onset. Recognizing hypothyroidism and recalling symptoms in child-hood, even if often non-specific, is fundamental for avoiding diagnosis delay.

DUOX2/DUOXA2 mutations frequently cause congenital hypothyroidism that evades detection on newborn screening in the UK

Patients with mutations in the dual oxidase 2 (DUOX2 ) gene – encoding a NADPH oxidase that generates hydrogen peroxidase for iodide organification – have been repeatedly reported as not being detected by neonatal screening because it causes only mild hyperthyrotropinemia at birth. Here, Peters et al. determined the incidence of DUOX2 and dual oxidase 2 maturation factor (DUOXA2 ) mutations in patients with borderline blood spot TSH values. In a retrospective genetic study in 52 patients with thyroid gland in situ and borderline TSH, they detected a surprisingly high incidence (50%) of DUOX2 or DUOXA2 mutations. The key characteristic of mutation positive vs. mutation negative patients during the neonatal period was a significantly higher TSH on venous confirmatory testing or on second blood spot screening than on initial screening and lower mean FT4 values despite mild hyperthyrotropinemia.

Treatment of Hypothyroid Patients With L-Thyroxine (L-T4) Plus Triiodothyronine Sulfate (T3S). A Phase II, Open-Label, Single Center, Parallel Groups Study on Therapeutic Efficacy and Tolerability.

Sodium salt of levothyroxine (L-T4) is the treatment of choice of hypothyroidism. Yet, L-T4 monotherapy produces supoptimal 3,5,3′-triiodothyronine (T3)/T4 ratio in serum, as compared to normal subjects, and a minority of hypothyroid individuals on L-T4 complain for an incomplete well-being. Orally administered 3,5,3′-triiodothyronine sulfate (T3S) can be converted to T3 in humans, resulting in steady-state serum T3 concentrations for up to 48 h. In this study (EudraCT number 2010-018663-42), 36 thyroidectomized hypothyroid patients receiving 100 (group A), 125 (group B), or 150 μg (group C) L-T4 were enrolled in a 75 days study in which 25 μg L-T4 were replaced by 40 μg of T3S. A significant, progressive reduction in mean FT4 values was observed, being the largest in the group A and the smallest in group C, while no relevant variations in FT3 and total T3 serum values were observed in the three groups. TSH serum levels increased in all groups, the highest value being observed in group A. Lipid parameters did not show clinically significant changes in all groups. No T3S-related changes in the safety laboratory tests were recorded. No adverse event was judged as related to experimental treatment, and no patient discontinued the treatment. Twelve patients judged the L-T4+T3S treatment better than L-T4 alone, while no patient reported a preference for L-T4 over the combined treatment.In conclusion, the results of this study indicate that a combination of L-T4+T3S in hypothyroid subjects may allow mainteinance of normal levels of serum T3, with restoration of a physiological FT4/FT3 ratio and no appearance of adverse events. Further studies are required to verify whether the LT4+T3S chronic combined treatment of hypothyroidism is able to produce additional benefits over L-T4 monotherapy.

Hypothyroidism in Children Beyond 5 y of Age: Delayed Diagnosis of Congenital Hypothyroidism

To determine the frequency of undiagnosed congenital hypothyroidism (CH) and its manifestations in hypothyroid children presenting beyond 5 y of age. Retrospective analysis of records of children with hypothyroidism more than 5 y of age at presentation between October 1997 and April 2010. Three hundred twenty children were diagnosed with hypothyroidism. Ninety-four (29.3%) were ≥5 y at presentation. Of these, CH was diagnosed in 34 (36.1%) and acquired hypothyroidism (AH) in 60 (63.9%). Symptoms of CH were noted at a mean age of 35.3±25.9 mo (range 12-132 mo) while the mean age at presentation was 86.6±35.3 mo (range 60-216 mo). The mean interval between onset of symptoms and diagnosis was nearly 51 mo. The mean duration of symptoms before diagnosis in children with AH was significantly shorter (8 mo, p<0.001). The main presenting complaints in children with CH and AH were growth delay (100%) and thyroid swelling (65%) respectively. Mean fT4 values in CH and AH at presentation were 0.23 and 0.34 ng/dL respectively (p=0.019). Children with CH had significantly higher TSH values (377.4 mIU/L) as compared to those with AH (151.4 mIU/L) (p=0.002) and had significantly delayed bone age (mean difference in chronological age and bone age 4.9 y in CH vs. 2.0 y in AH, p<0.01). Most common cause of CH in this group was thyroid dysgenesis (51.8%), followed by agenesis (25.9%) and dyshormonogenesis (22.2%). In absence of a universal screening program, diagnosis of CH, an important cause of preventable mental retardation is often delayed in India.

Effects of rehabilitation treatment on thyroid function

The aim of the study was to evaluate the effects of an intensive rehabilitation programme on thyroid metabolism, the relationship between disability and thyroid hormone level, and the occurrence of nonthyroidal illness syndrome (NTIS) before and after rehabilitation. This was a clinical prospective study. Orthopaedic surgery patients (n = 82) were classified into two groups: patients in whom early active mobilization and walking were possible (walking group, WG, n = 45), and patients in whom these were not recommended (nonwalking group, NWG, n = 37). Levels of free T3 (fT3), fT4, TSH and rT3 were measured before and after surgery, and then at 1, 3, 7, 14 and 30 days from the beginning of rehabilitation. Personal, nutritional and clinical data were acquired for all patients. The Barthel Index (BI) was used to assess disability before and after rehabilitation. Immediately after surgery, both groups of patients showed a significant decrease in mean fT3 concentrations and a significant increase in rT3; mean fT4 values decreased significantly only in NWG patients. Once rehabilitation had been completed, fT3 and rT3 levels returned to baseline values in WG patients. In NWG patients mean fT3 and fT4 levels continued to decrease significantly and rT3 values remained significantly high until the end of rehabilitation. NTIS occurred in 38% of the NWG patients. No significant changes in TSH levels were observed in either group. Finally, we observed a direct correlation between fT3 levels and the BI in WG patients. Our data suggest that early patient mobilization and physical activity during an active and intensive rehabilitation programme induce recovery of thyroid function and avoid occurrence of NTIS.

Free thyroxine assessed with three assays in sera of patients with nonthyroidal illness and of subjects with abnormal concentrations of thyroxine-binding proteins

Three methods for estimating free thyroxine (FT4) in serum were studied: equilibrium dialysis, the SPAC-ET FT4 radioimmunoassay kit, and the Amerlite MAB FT4 luminometric assay. Serum samples from 10 subjects with above-normal thyroxine-binding globulin (TBG), 6 with low TBG, 30 with familial dysalbuminemic hyperthyroxinemia (FDH), 13 with nonesterified fatty acids (NEFA) concentrations in serum > 1.0 mmol/L, and 178 patients with various degrees of nonthyroidal illness (NTI) were measured and compared with samples from 42 euthyroid blood donors. The Amerlite MAB FT4 assay compared well with equilibrium dialysis, whereas the SPAC-ET assay averaged 40% lower. All three assays were not influenced by changes in TBG and showed no or only little changes in the presence of NEFA. Mean FT4 values in the FDH samples were somewhat higher than in controls when measured with the SPAC-ET assay, about equal with equilibrium dialysis, and somewhat below the mean control value with the Amerlite MAB FT4 assay, although individual results were within the control reference range. In NTI patients, no FT4 values were below the control reference range by the Amerlite MAB FT4 assay, 4 of 178 were below this range by equilibrium dialysis, and 1 of 178 was below this range by the SPAC-ET assay. In all assays a large proportion of the NTI samples showed FT4 values above the control reference range, a result that will interfere with the efficacy of these assays for assessing thyroid function in NTI patients.

Comparison of four methods for free thyroxin

We performed a limited evaluation of four free thyroxin (FT4) reagent kits: the Amerlex-M (AFT4), the Amerlite (LFT4), the MagicLite (MFT4), and the GammaCoat two-step RIA (GFT4). FT4 was measured in specimens from 201 subjects: 19 healthy controls, 14 patients who were thyrotoxic, 13 who were hypothyroid, 59 who had a past history of thyroid disease, seven with thyroxin autoantibodies, seven who were taking amiodarone, and 82 who had no clinical indication of thyroid hormone abnormality. Of these 201 subjects, 78 had a low serum albumin (less than 35 g/L) and 27 had severe nonthyroidal illness. We also investigated 60 pregnant subjects. We found no correlation between thyroxin-binding globulin (TBG) and FT4 in any of the assays, and only the AFT4 method showed a significant correlation with albumin concentrations. The presence of autoantibodies to thyroxin affected the results of all methods except the GFT4 method. All methods showed a decrease in mean FT4 values in late pregnancy. Correlation of patients' clinical state and FT4 results suggested that the reference ranges published by the manufacturers need to be modified for our laboratory.

Comparison of serum free thyroxine measurements by chemiluminescence and equilibrium dialysis

A study of 239 patients compared free thyroxine (FT4) measurements made by equilibrium dialysis (ED) with measurements made using the Magic Lite FT4 chemiluminescence (CI) immunoassay (Ciba Corning Immunodiagnostics). Patient groups: 41 normals; 27 hyperthyroid; 29 hypothyroid; 37 sick euthyroid; 10 chronic renal failure (CRF) and 25 pregnant patients; 13 oestrogen; 10 heparin; 12 salicylate; and 9 dilantin-treated patients; 3 lipaemic; 5 haemolysed; 6 hyperbilirubinaemic patients; 6 low thyroid binding protein (TBP) and 6 high TBP level patients. The two assays gave comparable results in most groups. Both assays tended to give elevated values in heparinized patients but FT4-ED results were more obviously affected. Pregnant patients and women on oral oestrogen had higher mean values with FT4-ED. In both assays the sick euthyroid and CRF patients had mean FT4 values similar to healthy euthyroid patients; the range of values in sick euthyroid and CRF patients was similar in both assays but wider than in healthy euthyroid patients. A supplemental study of 81 unselected acutely ill patients using FT4-Cl alone confirmed the wider range of values to be anticipated in sick euthyroid patients.

Free thyroxine, free triiodothyronine, and thyrotropin concentrations in hypothyroid and thyroid carcinoma patients receiving thyroxine therapy.

Free thyroxine (FT4) and free triiodothyronine (FT3) concentrations in serum were measured by direct equilibrium dialysis methods in patients receiving thyroxine replacement or suppression therapy. Four of 50 hypothyroid patients euthyroid on replacement therapy (mean thyroxine dose 120 micrograms/day) had supranormal FT4 concentrations, whereas the FT3 concentrations were normal in all. Forty-one of 56 operated thyroid carcinoma patients on suppressive therapy (mean thyroxine dose 214 micrograms/day) had raised FT4 concentrations, whereas the FT3 concentrations was elevated in only one patient. There was a large difference in mean FT4 values for hypothyroid and thyroid carcinoma patients (17.2 vs 29.5 pmol/l), whereas the difference in mean FT3 values was small (5.0 vs 6.1 pmol/l), suggesting a decreased peripheral conversion of T4 to T3 with increasing concentrations of FT4. Serum TSH concentrations, as determined by an immunoradiometric assay, varied from less than 0.02 to 11.9 mU/l in treated hypothyroid patients; 21 patients (42%) had values outside the reference limits. As a single test, serum TSH is therefore not very useful for the assessment of adequate thyroxine dosage in patients with primary hypothyroidism. In thyroid carcinoma patients, the TSH concentrations were less than 0.18 mU/l; 45 patients had values less than 0.02 mU/l indicating sufficient suppression of TSH secretion in the majority of cases. On the basis of these results we recommend the combination of FT3 and TSH tests for monitoring thyroxine replacement and suppression therapy. FT4 appears less useful than FT3 for this purpose even if special reference values values were adopted for each patient group.

Effect of heparin on serum free thyroxine linked to post-heparin lipolytic activity.

A possible association between free T4 (fT4) changes, occurring after heparin administration, and the post-heparin lipolytic activity, i.e., the release of lipases and the lipolysis of triglycerides to non-esterified fatty acids (NEFAs) was studied. In 19 patients heparin increased mean fT4 values obtained by equilibrium dialysis from 23.4 to 38.6 pmol/l (P less than 0.01) and mean fT4 values measured by GammaCoat two-step RIA from 17.0 to 24.1 pmol/l (P less than 0.01), the results of the two methods agreeing well (rs = 0.88). Concurrently, NEFAs increased from a mean of 0.55 to 2.20 mmol/l (P less than 0.01) and fT4 increases were significantly correlated with post-heparin NEFAs (rs = 0.69, P less than 0.001). In vitro addition of palmitic acid to sera increased fT4 concentrations to values similar to those observed in vivo. Post-heparin fT4 increases were also strongly correlated to the concentrations of triglycerides (rs = 0.63, P less than 0.01). Hypertriglyceridaemia was associated with pronounced fT4 increases after heparin administration, and normolipidaemia with moderate or no changes. These results suggest that the effect of heparin on fT4 is linked to the activation of lipases by heparin and is mediated by NEFAs, which, at high concentrations, compete with thyroxine for binding proteins.