Mean T4 Levels Research Articles

Factors Influencing Peripheral Conversion of Thyroxine to Tri-Iodothyronine in Athyreotic Individuals during Levothyroxine Replacement

Background: Tri-iodothyronine (T3) is the main active hormone, and 20% of this is derived from the thyroid gland and 80% is from the peripheral tissue according to 5'-monodeiodination of thyroxine (T4). In the previous studies, normal T3 levels were achieved with traditional levothyroxine (LT4) therapy alone in athyreotic patients, but there has been no data about the factors influencing peripheral conversion of LT4. The aim of this study was to determine the factor(s) influencing peripheral conversion of LT4 to T3 in athyreotic patients during LT4 replacement. Methods: The patients who underwent total-thyroidectomy for any cause, and mostly for thyroid cancers, at Asan Medical Center between 2000 and 2008 were enrolled. The free T4, T3 and thyroid stimulating hormone (TSH) levels and age, gender, weight, height, body mass index (BMI) and the T4 dose were measured. Only patients with normal ranges of free T4 and TSH were included in the analysis. Results: A total of 143 patients were enrolled. The mean T3, free T4 and TSH levels were 143.7 ng/dL, 1.4 ng/dL and 1.6 /mL, respectively. The mean weight and BMI were 62.9 kg and 24.6 kg/, respectively. We divided them into two groups according to the serum T3 level and we compared the characteristics of the groups. There were no differences in age, the gender distribution, the T4 dose/weight and the BMI between the low T3 group (T3 122 ng/dL, n = 14) and the normal T3 group (T3 > 122 ng/dL, n = 129). In the low T3 group, the mean body weight was significantly lower than that of the normal T3 group ( vs. , respectively, P = 0.025). Conclusion: Lean body mass seems to be an important factor for determining the peripheral conversion of T4 to T3 in human. This suggest that a combination of T3/T4 is better than T4 only when we treat the patients with hypothyroidism and who have a negligible amount of functioning thyroid tissue, if they have a low lean body mass.

Serum thyroid hormone profile in critically III children

To study thyroid hormone profile in critically ill children and its correlation to disease severity and clinical outcome. Total serum triiodothyronine (T3), thyroxine (T4) and TSH were estimated at admission and discharge from PICU/ just before death. Mean T3 levels in cases were significantly lower than controls and lower in patients who expired, both at admission and just prior to death. Mean T4 levels were lower in cases, and just prior to death. Mean TSH levels were not different in cases and controls; or in survived and expired cases. When both T3 and T4 are low, mortality risk increases 30 times. Serum T3, T4 and TSH values improved in patients who survived unlike in those who expired. Age, sex, duration of hospital stay, ventilation, inotropic support, and PICU stay did not show any correlation with patient outcome or thyroid hormone profile. PRISM score at 24 hours and T4 levels in the second sample were significant predictors of survival. T3 levels reflect the patient's clinical status, T4 levels can predict survival.

Thyroid Hormone Levels Associated with Active and Passive Cigarette Smoking

Active and passive cigarette smoking are a risk factor among women of reproductive age-leading to reproductive health morbidity, including fetal and infant death and developmental problems with the newborn. However, the underlying physiological mechanisms for these ill-effects are not fully understood. Smoke exposure may affect various metabolic and biological processes, including hormone biosynthesis and secretion, interfere with thyroid hormone release, binding, transport, storage, and clearance, associated with adverse effects on the thyroid resulting in changes in circulating hormone concentrations. We measured and compared serum thyroid hormone and thyroid stimulating hormone (TSH) concentrations in active, passive, and nonsmokers and determined their association with cigarette tobacco smoke exposure. We use a comprehensive approach to assess the interrelationships between active and passive tobacco smoke exposure and thyroid hormone levels by employing innovative hormone analysis techniques. Serum was obtained from women (18-44 years of age). Thyroxine (T4), triiodothyronine (T3), and cotinine concentrations were quantified using isotope dilution high performance liquid chromatography tandem mass spectrometry, and TSH concentrations by chemiluminescence. Serum concentrations of the various hormones of active smokers, passive smokers, and nonsmokers (nonexposed), respectively, were as follows. Median TSH concentrations were 1.02, 1.06, and 1.12 mIU/L (p < 0.001 for the comparison of each group with the other two groups), and mean TSH levels were 1.40 mIU/L, confidence interval (CI) 0.07-6.83 mIU/L; 1.30 mIU/L, CI 0.25-3.01 mIU/L; and 1.50 mIU/mL, CI 0.71-4.00 mIU/L. Median serum T4 concentrations were 7.6, 7.9, and 8.7 microg/dL, and median serum T3 concentrations were 92.0, 84.0, and 102.0 ng/dL (p < 0.0001). Mean T3 levels were 99.1 ng/dL, CI 52.1-204.3 ng/dL; 87.6 ng/dL, CI 40.1-160.2 ng/dL; and 106.6 ng/dL, CI 46.4-175.0 ng/dL. Pair-wise comparisons of the three study groups indicate statistically significant differences in serum T4 (p < 0.01) and T3 (p < 0.001) means for the comparison of each group with the other two groups. This study is unique in examining the association of serum cotinine and thyroid hormone concentrations using liquid chromatography tandem mass spectrometry in women smokers, passive smokers, and nonsmokers. Active and passive exposure to cigarette tobacco smoke is associated with a mild inhibitory effect on the thyroid reflected in higher serum T4 and T3 in nonsmokers compared to smokers in this cohort of women.

Gestation-Specific Thyroxine and Thyroid Stimulating Hormone Levels in the United States and Worldwide

Euthyroid women experience dramatic changes in the demand for thyroid hormone production as early as the first trimester of pregnancy. These changes are important for fetal neurodevelopment and organ development as well as maternal health and succesful full term pregnancy. Therefore, gestation-specific reference intervals assist in appropriate clinical management of thyroid disease in pregnancy to ensure maternal and fetal health. To determine trimester-specific levels of serum thyroxine (T4) and thyroid stimulating hormone (TSH) in the U.S. population based on the National Health and Nutrition Survey III and compare these with published trimester-specific T4 and TSH means and medians obtained in other countries worldwide. Trimester-specific means and medians for T4 and TSH were determined for the U.S. population based on the National Health and Nutrition Survey III database (1988-1994). These were compared with trimester-specific means and medians of other countries in the published literature. Mean serum T4 levels for the U.S. population were 141.35, 152.95, and 142.65 nmol/L in the three trimesters, respectively, whereas mean serum TSH levels were 0.91, 1.03, and 1.32 mIU/L. Gestation-specific mean T4 and TSH levels for the representative U.S. population are well within the trimester-specific reference intervals. T4 and TSH measured during pregnancy in longitudinal and cross-sectional studies of populations worldwide demonstrate that, in some populations, T4 and TSH levels are outside the normal trimester-specific reference intervals.

Postnatal thyroid hormones for preterm infants with transient hypothyroxinaemia

Extremely premature infants are at risk of transient hypothyroxinaemia in the first weeks after birth. These low thyroid hormone levels are associated with an increased incidence of neonatal morbidity, mortality and longer term developmental impairments. Thyroid hormone therapy might prevent these problems. To determine the evidence for thyroid hormone therapy in preterm infants with transient hypothyroxinaemia (low thyroid hormone level, normal TSH) for improvement of neonatal outcomes and neurodevelopment. Searches were performed of The Cochrane Central Register of Controlled (CENTRAL, The Cochrane Library, Issue 1, 2006), MEDLINE (1966 - March 2006), PREMEDLINE (March 2006), EMBASE (1980 - March 2006), previous reviews including cross references, abstracts and conference proceedings, supplemented by requests to expert informants. Trials enrolling preterm infants with transient hypothyroxinaemia (low thyroid hormone level, normal TSH level) in the neonatal period, using random or quasi-random patient allocation to thyroid hormone therapy compared to control (placebo or no treatment). Independent assessment of trial quality and data extraction by each review author. Synthesis of data using relative risk (RR) and weighted mean difference (WMD) using standard methods of the Cochrane Collaboration and its Neonatal Review Group. Only one study was eligible. Chowdhry (1984) enrolled 23 infants < 1250 g and 25 - 28 weeks gestation with transient hypothyroxinaemia (serum total T4 </=4 mug/dl and TSH </= 20 IU/L). Infants were randomised to thyroxine 10 mug/kg/day or placebo beginning on day 15 and continuing daily for seven weeks. Chowdhry (1984) reported no neonatal mortality and one infant death in each group prior to discharge. No significant difference was reported in CLD at 28 days or 36 weeks, patent ductus arteriosus, necrotising enterocolitis, retinopathy or prematurity, weight gain, growth in head circumference or length. No significant difference was reported for mean T4 levels between thyroxine and placebo treated infants on day 21, 35, 49, 63 and 77 after birth. Free T4 was not measured. Neurodevelopmental follow up was inadequate to draw any conclusions from. There is insufficient evidence to determine whether use of thyroid hormones for treatment of preterm infants with transient hypothyroxinaemia results in changes in neonatal morbidity and mortality, or reductions in neurodevelopmental impairments. Further research is required.

Euthyroid sick syndrome and cardiac failure in Zaria, Nigeria

The study was aimed at establishing the existence of sick euthyroid syndrome in our patients with cardiac failure and to find out whether the syndrome in the our patients has a peculiar pattern Thirty subjects diagnosed with cardiac failure in NYHA class 3 and 4 were studied; they had clinical evaluation, electrocardiograph, chest radiograph and echocardiograph. The biochemical investigation included urea, electrolyte, and creatinine, thyroid function test (T3, T4 and TSH). Thirty individuals who served as control (age and sex matched) also had similar evaluation to the subjects. The subjects' ages ranging from 17 to 85 years and a mean of 51.0 +/- 15.8 years compared to controls with a mean age of 48.9 +/- 8.1 years (p < 0.1). Twenty-two and eight patients were in NYHA class3 and 4 respectively. The subjects had a lower mean T3 than controls of 1.42 +/- 0.07 ug/l and 2.3 +/- 1.0 ug/l respectively and p < 0.001. The mean T4 levels were higher in the subjects than controls (85.4 +/- 26 ug/l and 70.0 +/- 1.7 ug/l respectively and p < 0.001) but TSH levels were similar in the two groups. The subjects had higher mean values of LAD, aortic root diameter, IVSD, LVIDD, LVPW, EDV ESV, LVM and LVMI (p < 0.05). The LV ejection fraction and fractional shortening were lower in subjects than controls (p <0.01). Six, seventeen and seven subjects had diastolic, systolic and combined diastolic-systolic dysfunction on echocardiography respectively. There was a positive correlation between T3 with duration of cardiac failure and ejection fraction (p < 0.05). There was a negative correlation between T3 and LVM, LVMI, LVIDD, EDV, LAD and cardio-thoracic ratio. The levels of T4 showed a positive relationship with LAD and CTR. Partial correlation was statistically significant between T3 and duration of cardiac failure, duration of aetiology of cardiac failure and LVM. The various forms of cardiac failure (diastolic, systolic and combined diastolic-systolic dysfunction) showed no statistically significant difference in mean levels of T3, T4 and TSH. Euthyroid sick syndrome is also seen in Nigerians with cardiac failure as reported elsewhere and the levels of T3 seemed to be inversely proportional to LAD, CTR, LVIDD, LVM and LVMI. Serum T3 levels are also directly proportional to EF and FS. Low serum levels of T3 with normal T4 and TSH is associated with severe cardiac failure.

Perfil dos hormônios tireoidianos nas síndromes coronarianas agudas

To describe thyroid hormone profile in patients with acute coronary syndromes (ACS), divided into two groups: 1) unstable angina and/or non-ST-segment elevation acute myocardial infarction (UA/NSTEMI); 2) ST-segment elevation acute myocardial infarction (STEMI), as well as in patients that progressed or not to death, according to the groups. Seventy ACS patients admitted to the coronary care unit of the Hospital dos Servidores do Estado, Rio de Janeiro, were prospectively studied. Blood samples were collected on day 1 and on days 4 and 7 following admission. Clinical evaluation and electrocardiograms were performed during hospitalization. Of the 70 patients admitted, 13 (18.6%) had "euthyroid sick syndrome" (ESS), a condition characterized by decreased serum T3 and/or free T3, increased serum reverse T3 (rT3), plus normal serum TSH, T4, and free T4. Patients belonging to the STEMI group showed early elevations, in addition to higher mean reverse T3 (rT3) and lower mean T3 and free T3 levels. In coronary heart disease patients that progressed to death, hormonal findings were consistent with those found in the ESS, with more expressive rT3 and T3 mean values. Our results show the importance of recognizing the "euthyroid sick syndrome" in coronary heart disease patients, suggesting an association with poorer prognosis in patients with acute coronary syndrome.

Tc]-99m Thyroid Scintigraphy in Congenital Hypothyroidism Screening Program

The aetiology of congenital hypothyroidism (CH) may be important in determining disease severity, outcome and treatment schedules because athyroid patients need higher treatment doses and close monitoring particularly early in life. The aim of this study was to evaluate thyroid scintigraphy (TS) findings in infants with CH and to determine the relationship of serum TSH and T4 values with thyroid agenesia, in an attempt to identify factors that may detect thyroid agenesia before treatment. Since August 2002 to April 2005, screening program for CH was carried out in the Isfahan University of Medical Sciences and Health Services, Isfahan, Iran. Screening was performed by measuring both the serums T4 and TSH concentration at day 3-7 of birth. Full-term newborns were recalled based on a serum TSH >20 mIU/l or serum T4 < 6.5 microg/dl and premature newborns based on T4 level by weight and TSH level by age. After repeating the laboratory test and clinical evaluation, Tc-99m TS was recommended for all infants with suspected CH before thyroxin replacement therapy. On the basis of Tc-99m TS, the thyroid gland was classified as normal scan, ectopic, goiter and athyrosis. TS results were compared with serum T4 and TSH levels. Of 93 381 newborns screened over a period of nearly 3 years, 262 neonates were found to have CH. The overall incidence of CH was 1 : 357 live births with a female/male ratio (F/M) of 1.4/1. Thyroid scan was performed on 116 (54%) of the infants with CH; of them, 33 cases (28.4%) were athyrotic (F/M = 0.8/1) while seven infants (6%) had ectopic thyroid (F/M = 1.3/1) and 76 cases (65.6%) had a normal thyroid scan (F/M = 1.5/1). Infants with the absence of thyroid in TS had significantly higher TSH value in comparison with those with ectopic or normal TS (116.3 +/- 109.64 vs. 108.10 +/- 62.92 or 55.35 +/- 48.26 mIU/l, respectively, P < 0.0001). Although not statistically different, the mean T4 level was higher in normal TS group than in ectopic and athyrotic groups (8.03 +/- 3.48 vs. 6.36 +/- 5.57 or 5.04 +/- 3 microg/dl, respectively, P = 0.09). We conclude that Tc-99m TS is a useful diagnostic tool for the initial investigation of suspected CH and considering the correlation of TS results with blood TSH levels, proper management and close monitoring of hypothyroid infants with severe hormonal alterations is necessary for the detection of thyroid agenesia.

Regulation of Graves’ Hyperthyroidism with Naturally Occurring CD4+CD25+ Regulatory T Cells in a Mouse Model

Graves' hyperthyroidism can be efficiently induced in susceptible mouse strains by repeated immunization with recombinant adenovirus coding the TSH receptor (TSHR). This study was designed to evaluate the role(s) played by naturally occurring CD4(+)CD25(+) regulatory T cells in the development of Graves' hyperthyroidism in resistant C57BL/6 and susceptible BALB/c mice. Depletion of CD4(+)CD25(+) T cells rendered some C57BL/6 mice susceptible to induction of hyperthyroidism. Thus, hyperthyroidism developed in 30% of the CD4(+)CD25(+) T cell-depleted C57BL/6 mice immunized with adenovirus expressing the TSHR A-subunit (AdTSHR289) vs. 0% of those immunized with AdTSHR289 alone. This immunological manipulation also enhanced disease severity in susceptible BALB/c mice, as reflected by a significant increase in mean T(4) levels by CD4(+)CD25(+) T cell depletion. The immunoenhancing effect of CD4(+)CD25(+) T cell depletion appears to be attributable to an increase in thyroid-stimulating antibody production and/or a decrease in thyroid-blocking antibody synthesis, but not immune deviation to either T helper 1 or 2 cells. Interestingly, unlike BALB/c mice, some hyperthyroid C57BL/6 mice showed some intrathyroidal lymphocytic infiltration with follicular destruction. These results indicate that CD4(+)CD25(+) T cells play a role in disease susceptibility and severity in adenovirus-TSHR-induced Graves' hyperthyroidism. Overall, the imbalance between effector and regulatory T cells appears to be crucial in the pathogenesis of Graves' disease.

Effect of androgen deprivation therapy in the thyroid function test of patients with prostate cancer

We have assessed the effect of androgen deprivation therapy (ADT) in the thyroid function test in prostate cancer patients. Serum levels of tri-iodothyronine (T3), thyroxine (T4), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were determined in a cross-sectional study that included 279 patients diagnosed with prostate cancer. A subset of 96 patients free of prostate-specific antigen relapse after radical prostatectomy became a control group and 183 patients under continuous ADT formed the study group. Sixty-four patients out of the study group were treated with luteinizing hormone-releasing hormone (LHRH) agonist and 119 with LHRH agonist plus bicalutamide. The average time of ADT was 42.5 months (3-218). Results were as follows. Mean T3 level was 122.7 ng/dl (72.6-213.0) in the control group and 123.8 ng/dl (64.4-228.2) in patients under ADT, p=0.472. Mean T4 level was 7.66 (1.81-4.30) and 7.66 microg/dl (3.60-13.30), respectively, p=0.884. Mean TSH level was 1.58 (0.44-11.70) and 1.81 mU/dl (0.15-6.58), respectively, p=0.007. Mean FT4 level was 1.24 (0.80-1.90) and 1.18 ng/dl (0.80-1.90), respectively, p=0.018. No statistically significant differences between the T3, T4, TSH and FT4 serum levels were detected according to the modality of ADT. The serum level of TSH was higher than 5 mU/l in six patients (2.1%); however, all cases had a normal FT4 serum level. This mild hypothyroidism was detected in two of the 96 patients of the control group (2.1%) and in four of the 183 under ADT (2.2%). Our data show that ADT seems to alter the thyroid function test. A statistically significant increase in TSH serum level and a decrease in FT4 serum level were detected in patients under ADT. However, only a mild hypothyroidism was detected in about 2% of the patients with prostate cancer, independently of ADT.

Ist TSH ein geeigneter Indikator für eine adäquate Schilddrüsenhormon-Substitution?

The objective of this study was to evaluate parameters of thyroid function and indices of peripheral thyroid hormone action (such as SHBG) in patients whose hypothyroidism was considered well controlled under current criteria. Eighty-five patients with T4-treated hypothyroidism, 28 of whom had athyria, were compared with 114 normal individuals with the same TSH levels. T3 levels were significantly lower in hypothyroidism although mean T4 and fT4 levels were significantly higher. Furthermore, mean SHBG levels were significantly lower in hypothyroidism independently of age. The difference remained when stricter criteria for adequate treatment were applied (TSH < 2.5 microgU/ml). Significant negative correlations were found between logTSH and T3. The slopes of the regression lines of T3 to TSH were significantly different in the control group and the hypothyroid group: thus, for the same TSH levels, T3 levels were lower in the hypothyroid group. We conclude that patients with T4-treated hypothyroidism have lower T3 levels, lower T3/T4 ratio and lower SHBG than normal individuals with the same TSH, perhaps indicating relative tissue hypothyroidism in the liver. TSH levels used to monitor substitution, mostly regulated by intracellular T3 in the pituitary, may not be such a good indicator of adequate thyroid hormone action in all tissues. The co-administration of T3 may prove more effective in this respect, provided novel suitable preparations are developed. Until this is accomplished, substitution in hypothyroidism should aim at low normal TSH, to ensure normal T3 levels.

Urinary iodine and other iodine deficiency indicators in a sample of school-age children in Egypt

Sufficient data relating urinary iodine excretion in children to other iodine deficiency indicators are lacking in Egypt. We assayed urinary iodine concentration and serum levels of thyroid stimulating hormone (TSH), thyroglobulin, free triiodothyronine (T3) and free tetraiodothyronine in 99 school-aged Egyptian children. Goitre was found in 25 children. Median urinary iodine concentration was 70 microg/L. We found mild iodine deficiency (50-99 microg/L) in 60.6 % of the children and moderate to severe deficiency (< 50 microg/L) in 31.3%. The latter showed a high frequency of goitre and elevated mean serum free T3, TSH and thyroglobulin levels. Individual urinary iodine excretion rates vary, therefore these other indicators could help in screening for iodine deficiency at an individual level, especially in moderate to severe deficiency.

Left ventricular systolic and diastolic functions in children living in a moderate-severe iodine deficiency area.

Although the effects of impaired thyroid functions on the cardiovascular system is well known, there is no report investigating left ventricular functions in children with iodine deficiency. We evaluated left ventricular functions in children living in a moderate-severe iodine deficient area of northern Turkey. Of 40 children, 13 had stage I, 19 had stage II and eight had stage III goiter. None of the children had clinical signs of hypothyroidism, hyperthyroidism or cardiac dysfunction. Urinary iodine concentration decreased significantly from mild (Group 1) to moderate (Group 2) and severe (Group 3) iodine deficient groups (p <0.05). Mean serum free T3 levels did not differ significantly between the groups. However, a significant difference in mean serum free T4 level was found between Groups 1 and 2 (p <0.05), but remained in the normal range. Although the mean serum TSH level differed significantly between Group 1 and Group 3 and Group 2 and Group 3 (p <0.05), mean values were in the normal range. Mean left ventricular ejection fraction, shortening fraction and diastolic filling parameters did not differ significantly between groups. In conclusion, in case of preserved thyroid hormone levels, a moderate-severe iodine deficiency does not seem to affect left ventricular functions.

Impact of lead exposure on pituitary-thyroid axis in humans.

Thyroid function tests (serum levels of thyroxine-T4, triiodothyronine-T3 and thyroid stimulating hormone-TSH) were performed in fifty-eight men (mean age: 31.7 +/- 10.6 years; mean duration of lead exposure: 156.9 +/- 122.7 months). These subjects were exposed to lead either as petrol pump workers or automobile mechanics. The mean whole blood lead (Pb-B) levels were 2.49 +/- 0.45 micromole/l (51.90 +/- 9.40 microg/dl) in the lead exposed workers and were approximately 5 times higher than in the control (n = 35) subjects. No significant alteration was seen in their mean T3 and T4 levels as compared with the controls. Interestingly, T3 was significantly lower with the longer (210 months) exposure time in comparison with the group having shorter (29 months) exposure duration. The mean TSH levels were significantly (p < 0.01) higher in workers exposed in comparison with the control group. This rise in TSH was independent of exposure time, but it was definitely associated with the Pb-B levels. The increase being more pronounced with mean Pb-B levels of 2.66 +/- 0.2 micromole/l (55.4 +/- 4.25 microg/dl) when compared with the group having mean levels of 1.51 +/- 0.30 micromole/l (31.5 +/- 6.20 microg/dl). The rise is TSH associated with Pb-B levels was only statistical valid, however, the levels fall within the normal laboratory range. We thus conclude that the Pb-B levels of > or = 2.4 micromole/l (50 microg/dl) could enhance the pituitary release of TSH without having any significant alterations in the circulating levels of T3 and T4.

Topical iodine-containing antiseptics and subclinical hypothyroidism in preterm infants

The influence of topical iodine-containing antiseptics on thyroid function test results of premature infants was determined in two separate studies. Thyroxine and thyrotropin levels were measured on blood-spotted filter paper. Samples were obtained from 128 premature infants on their tenth day of life; the infants were treated in two neonatal intensive care units. Both units used similar treatment protocols; however, one routinely used topical iodinated antiseptic agents (n = 73), whereas the other used chlorhexidine-containing antiseptics (n = 55). There was no difference in the mean T4 levels between the two groups. The mean thyrotropin levels were elevated in preterm babies exposed to iodine (15.4 vs 7.8 mIU/L, p < 0.01). Among the iodine-exposed infants, elevated thyrotropin levels (> 30 mIU/L) were found in 13.7% of infants, compared with none in the chlorhexidine-treated group (p < 0.01). We then studied an additional 46 premature infants who were treated in one neonatal intensive care unit. Iodine-containing solutions were used in 24 infants and chlorhexidine was used in 22 infants. T4 and thyrotropin levels were measured weekly during the first 28 days, one every 2 weeks until the age of 60 days, and at the age of 90 days. Among iodine-exposed infants, 20.8% had thyrotropin values > 30 mIU/L, whereas none of the infants in the chlorhexidine group had elevated thyrotropin values (p < 0.05). The elevated thyrotropin levels correlated positively with the area of disinfection. Elevated urine iodine levels were present reflecting an abnormally high iodine absorption. This study suggests that iodine absorption from topical iodine-containing antiseptics may cause disturbances in thyroid function test results in premature infants. We recommend that caution be exercised in the use of iodine-containing antiseptics in premature infants.

Effects of iodine deficiency on insulin‐like growth factor‐I, insulin‐like growth factor‐binding protein‐3 levels and height attainment in malnourished children

The expression and synthesis of IGF-I and IGFBP-3 have been shown to be regulated by hormones and nutrition. We study the effects of malnutrition and iodine deficiency on these growth factors and the height attainment of a group of children. We measured serum IGF-I and IGFBP-3 levels in a group of Malaysian aborigine children from three jungle settlements; Sinderut and Pos Lanai are known for iodine deficiency and endemic goitre, and Gombak is an iodine replete area with better socioeconomic status. A total of 246 children were studied, 188 in the age group 4-10 years and 88 in the age group 11-15 years. All children were assessed anthropometrically and height standard deviation score (SDS) were calculated using the CDC Anthropometric Software package. Malnutrition was confirmed clinically and according to the WHO definition of malnutrition. IGF-I and IGFBP-3 were determined by radioimmunoassay, and T4 and TSH by immunoradiometric assay. Based on the height SDS, Sinderut and Pos Lanai children were significantly more malnourished and stunted than the Gombak children P = 0.0001). T4 levels were significantly lower (P = 0.0001) amongst the 4-10-years old Sinderut (81 +/- 2 nmol/l) than in Pos Lanai (101 +/- 3 nmol/l) or Gombak (123 +/- 3 nmol/l) children. Similar findings were also seen in the older children; mean T4 levels of those from Sinderut and Pos Lanai (83 +/- 3 and 88 +/- 4 nmol/l respectively), were low (P = 0.0001) compared to Gombak (118 +/- 3 nmol/l). Conversely, TSH levels in both age groups of Sinderut children were significantly elevated (P = 0.0001) (3.5 +/- 0.2 and 3.9 +/- 0.3 mU/l respectively) compared to age-matched groups from Pos Lanal (2.1 +/- 0.1 and 2.2 +/- 0.2 mU/l respectively) and Gombak (1.5 +/- 0.1 and 1.5 +/- 0.2 mU/l respectively). IGF-I and IGFBP-3 correlated significantly with the height SDS of the children, In both the 4-10 (r = 0.400, P = 0.0001 and r = 0.365, P = 0.0001 respectively) and 11-15 years age groups (r = 0.324, P = 0.002 and r = 0.533, P = 0.0001 respectively). Correlation between IGFBP-3 and T4 levels was more significant in the younger children (r = 0.412, P = 0.0001). Association between IGF-I and T4 levels was significant only in the 4-10 years age group (r = 0.237, P = 0.001). Varying duration and degree of exposure to malnutrition and iodine deficiency resulted in different mean levels of T4, TSH, IGF-I and IGFBP-3 in the three areas. The strong positive associations between IGF-I and IGFBP-3 levels and height SDS suggest that these biochemical measurements are indeed useful indicators of growth and nutritional status in children. The significant correlations between T4 and IGFBP-3 and IGF-1 suggests the importance of thyroid hormones in regulating the synthesis of these growth factors. The age-related increase of these growth factors even amongst malnourished, iodine deficient children implies that age-matched reference ranges are essential for proper evaluation of laboratory results.

832 Acute radiation-induced thyroiditis—A prospective study

Purpose We prospectively studied acute radiation-induced thyroid dysfunction by performing thyroid function tests. Materials and methods The subjects were 28 patients who underwent neck irradiation incidentally including the thyroid for various malignancies. The total dose absorbed by the thyroid was 4500–5000 cGy. Thyroid function tests included serum thyroid stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4). These data were obtained before irradiation, at 40 Gy irradiation, and 3 and 6 months thereafter. Results Mean TSH levels were 1.57,0.66, 1.34, and 6.23 μU/ml at preirradiation, 40 Gy irradiation, and 3 and 6 months after irradiation, respectively. The decrease in TSH levels at 40 Gy was significant (P = 0.0001, Wilcoxon signed-rank test). TSH levels significantly increased thereafter until 6 months (40 Gy vs 3 months:P = 0.001,3 months vs 6 months:P = 0.028). Mean T4 levels increased from 1.13 to 1.21 ng/ml during 40 Gy irradiation (P = 0.02). Conclusion The elevation of T4 and decrease in TSH observed at the time of irradiation was attributed to acute thyroid follicular cell destruction by irradiation.

Thyroid hormone changes in chronic spinal cord injury.

Spinal cord injury (SCI) impacts metabolic function and deranges various hormonal axes. Previous studies characterizing thyroid hormones in SCI reported depressed triiodothyronine (T3) and thyroxin (T4), primarily in acute tetraplegics. These studies cited an 11-13 percent incidence of low T3 syndrome (LT3S) in SCI patients, with an increased incidence in tetraplegics (20-36 percent). The purpose of this study was to evaluate thyroid function and determine the incidence and clinical relevance of LT3S in the chronic SCI population. Thyroid function tests were performed on 30 chronic SCI patients (14 tetraplegics and 16 paraplegics) and 30 age- and gender-matched controls. Mean T3 and T4 levels were significantly depressed in SCI patients relative to controls, while T3 resin uptake (T3RU) values were significantly elevated. LT3S only occurred in the SCI population with an incidence of 23.3 percent. SCI patients with LT3S did not differ significantly from those without in the level or completeness of injury, age or the interval since injury. They did, however, have co-existent pathology: decubiti, urinary tract infections, etc. When SCI patients with normal T3 were compared with controls, they still had depressed mean T3 levels. We conclude that LT3S occurs frequently in the chronic SCI population and suggest that depressed serum T3 levels may predispose SCI patients to sick euthyroidism in the face of minor pathologic insult.

Plasma T3 and T4 levels in a snake, Elaphe taeniura

The plasma thyroid hormones (TH) in the snake, Elaphe taeniura, were studied using RIA. Samples of plasma were obtained from untreated snakes in March, May and September as weU as thyroidectomized snakes in May. Scale biopsies were taken from each snake in order to see if there were any correlations of plasma T3 and T4 levels and epidermal changes during the sloughing cycle. Plasma samples were also taken from another snake species Ptyas korros and a chelonia sp. Clemmys mutica for comparison. Data showed that the plasma T3 and T4 levels of these reptilian species were very low (less than 1 nmol/1) and there were extensive individual variations (from below detection to 0.910 nmol/1). There were seasonal variations in these levels in E. taeniura. One week after thyroidectomy, the plasma levels of T3 and T4 could not be detected, suggesting that the thyroid gland is the only source of thyroid hormones in the snake. There was no correlation between mean plasma T3 and T4 levels during the resting and renewal phase. The extreme low level of plasma T4 preceding, and its absence following thyroidectomy which always precipitates, the renewal phase provide circumstantial support to the inhibitory role of TH on epidermal proliferation/differentiation in sloughing.

Cross-sectional and longitudinal study of the pituitary-thyroid axis in patients with thalassaemia major.

Thyroid dysfunction is known to occur frequently in thalassaemia major, but its prevalence and severity varies in different cohorts, and the long-term natural history is poorly described. We evaluated the pituitary/thyroid axis in thalassaemia major patients in a cross-sectional study and correlated abnormalities with indices of iron overload. Furthermore, the course of thyroid disease in thalassaemia major patients was assessed in a 15-year longitudinal study. Cross-sectional study: pituitary-thyroid axis function was examined in 37 patients (22 F, 15 M; aged 10-39 years, mean +/- SE = 21 +/- 1.4) out of a total of 43 who attended the Haematology and Endocrinology Clinics of Hadassah Hospital on a regular basis. The mean pretransfusion Hb level was 85 +/- 20 g/l, and all patients except one were treated with desferrioxamine (DF, mean +/- SE dose 20.2 +/- 2.6 mg/kg/day). Twenty-two had hypogonadotrophic hypogonadism (HH). Longitudinal study: 21 thalassaemia major patients were evaluated with TRH tests in 1976 and again in 1985. Fourteen of these and another eight were evaluated in both 1985 and 1991. Cross-sectional study: no patient had any clinical signs or symptoms of hypothyroidism; however, one had abnormally low T4, borderline low FT4 and normal T3 levels associated with an exaggerated TSH response to TRH consistent with mild hypothyroidism. This patient did not have a previous TRH test, but serial basal determinations over 7 years revealed a progressive decrease in thyroid function. Thirty-six patients had thyroid hormone levels within the normal range. Nine of these (24.3%) had only an exaggerated TSH response to TRH whereas seven others (19%) also had borderline elevated basal TSH levels. TSH response to TRH was not correlated with age, serum ferritin or liver function tests (ALT or GGT). Longitudinal study: mean TSH response to TRH decreased (P < 0.002), and mean T3 levels increased (P < 0.001) between 1975 and 1985. These findings are probably related to the initiation of DF treatment in 1981. During the last 6 years, four patients with previously normal TSH responses to TRH developed elevated peak TSH levels. Mean T3 concentrations decreased and TSH response to TRH increased significantly (P < 0.001 for both). (1) In this patient group the thyroid pituitary axis is less sensitive than the gonadal axis to iron-induced damage; only one out of 37 patients developed mild uncompensated hypothyroidism. (2) As opposed to the gonadal axis, the thyroid gland appears to fail before the central components of the axis. (3) Abnormal thyroid function may be reversible in the early stages. (4) Progression is variable, and it may take years to progress from normal to uncompensated hypothyroidism.