K. Liewendahl

THYROID FUNCTION TESTS IN PATIENTS ON LONG‐TERM TREATMENT WITH VARIOUS ANTICONVULSANT DRUGS

Thyroid function tests were studied in patients undergoing long‐term treatment with various anticonvulsant drugs. Previous reports that diphenylhydantoin induces a decrease in the serum concentrations of total and free thyroxine (T4) and tri‐iodothyronine (T3) without a change in the TSH concentration were confirmed. Diphenylhydantoin had no effect on reverse T3. Carbamazepine was also found to decrease serum T4, the free T4 index and T3 but, with the exception of T3, the decrease was smaller than that induced by diphenylhydantoin. Dipropylacetic acid did not influence the serum thyroid hormone concentrations, and neither did primidone. This demonstrates that the interaction between anticonvulsant drugs of different chemical structure and thyroid hormone metabolism is diverse. None of the drugs tested altered serum TSH or the T3 uptake test for the estimation of unsaturated thyroid hormone binding‐capacity in serum. These two tests are considered diagnostically more dependable than the measurement of thyroid hormones in serum when diphenylhydantoin and carbamazepine are administered.

Nuclear binding of triiodothyronine and thyroxine in lymphocytes from subjects with hyperthyroidism, hypothyroidism and resistance to thyroid hormones.

Binding of triiodothyronine (T3) and thyroxine (T4) to nuclei of intact human lymphocytes was studied. The binding characteristics were analysed by Scatchards method. In lymphocytes from euthyroid healthy subjects there was a single set of saturable nuclear T3 and T4 binding sites with an apparent mean equilibrium association constant of 3.3 X 10(10) l/mol and 1.7 X 10(10) l/mol, respectively. The estimated mean maximal specific binding capacity for T3 was 50 fmol/mg DNA and for T4 was 55 fmol/mg DNA, indicating that these two hormones may have a common receptor. In hyperthyroid and hypothyroid patients nuclear affinity for T3 and T4 was very similar to that for euthyroid reference subjects. In hyperthyroidism, T3 and T4 binding capacity was unaltered, whereas in hypothyroidism it was nearly twice as high as in euthyroidism. Lymphocytes from three members of a family with hereditary peripheral resistance to thyroid hormone action were studied. One set of saturable T3 and T4 nuclear binding sites with affinity constants similar to those in the euthyroid group was found. However, in these subjects the estimated binding capacity for T3 and T4 was rather low, indicating that the biochemical defect in this family might be a mild deficiency of nuclear receptor protein. Incubation with diphenylhydantoin and salicylate added in vitro did not alter the binding of T3 and T4 to lymphocyte nuclei. Nuclear binding was also not affected in patients receiving therapeutic amounts of diphenylhydantoin.

Abnormal thyroid function tests in severe non-thyroidal illness: diagnostic and pathophysiologic aspects

In vitro thyroid function tests were studied in twenty-three patients with serious non-thyroidal illness. All had reduced protein binding of serum thyroxine (T4) and serum triiodothyronine (T3) as reflected in increased T4 and T3 uptake tests. The mean T4-binding prealbumin (TBPA) capacity and concentration were about one third the normal levels, whereas the decrease in R4-binding globulin (TBG) was much smaller. Increased serum free fatty acids and reverse T3 were frequently observed, but in vitro displacement of thyroid hormones from their binding sites was achieved only with much high concentrations of these compounds. Other still unrecognized substances significantly inhibiting binding of thyroid hormones might, however, occur in sera of severely ill patients. Evidence in favour of this possibility was the disproportionately high serum T4 by TBG-binding assay relative to T4 by radioimmunoassay. In most of the patients the dual-stage free T4 was elevated, whereas the single-stage free T4 index (CT4I) was within the reference interval. However, neither of these indices reflected the moderately increased dialysable free T4 concentration very accurately. The free T3 index was depressed in most of the patients, whereas the dialysable free T3 concentration was not affected. For practical purposes the combination of normal serum T4 and CT4I in a severely ill patient indicates absence of an associated thyrometabolic disorders.

Thyroid Status of Patients Receiving Long‐Term Anticonvulsant Therapy Assessed by Peripheral Parameters: A Placebo‐Controlled Thyroxine Therapy Trial

Summary: Thyroid hormone concentrations and measures reflecting thyroid function were studied in sera from 35 patients receiving long‐term phenytoin (PHT) or carbamazepine (CBZ) therapy. The mean concentrations of T4 FT4 FT3 and rT3 but not T3 of these patients were significantly lower than those of 19 controls of similar age and sex distribution. The mean serum thyrotropin (TSH) concentration was slightly but significantly higher in patients than in controls, but the serum TSH response to TRH was not significantly increased. In patients, the higher mean clinical diagnostic index of hypothyroidism (CDI‐HT: ‐20.3 ±‐19.1 vs.‐33.7 ± 8.5, p < 0.05) and higher ratio of preejection period to left ventricular ejection time (PEP/LVET: 0.343 5 0.065 vs. 0.334 2 0.030, p < 0.05) than in controls were compatible with tissue hypothyroidism. However, comparison of the mean levels of alanine aminotransferase (ALAT), creatine kinase (CK), creatinine, triglycerides, cholesterol, high‐density lipoprotein (HDL) cholesterol, osteocalcin, procollagen type III aminoterminal propeptide, and somatomedin‐C showed no significant differences between patients and controls. The increased mean angiotensin convertase and sex hormone‐binding globulin (SHBG) levels, typical of hyperthyroidism, were probably caused by drug effects. Fourteen patients with a subnormal FT4 concentration in serum participated in a doubleblind thyroxine treatment cross‐over study. Neither the mean CDI‐HT score, nor the systolic time intervals were significantly different between the thyroxine and placebo periods. Five patients benefited subjectively from the treatment. On the basis of all data from the cross‐sectional and thyroxine treatment studies, we conclude that patients receiving anticonvulsant drugs chronically are eumetabolic and do not need thyroxine supplementation.

Effect of fatty acids on thyroid function tests in vitro and in vivo.

Addition of long-chain fatty acids to serum increased thyroxine (T4), measured by a competitive protein binding assay, and triiodothyronine (T3) uptake by Sephadex or resin (T3U tests). This is compatible with the assumption that fatty acids compete with thyroxine for binding sites on T4-binding proteins. When equimolar concentrations of various saturated and unsaturated fatty acids were added to serum it was observed that the effectiveness in raising tests based on protein binding of thyroid hormones incrreased serum T3 determined by radioimmunoassay (RIA). T4(RIA) was not significantly influenced by either saturated or unsaturated fatty acids. Serum T4(CPB) rose during storage at 22degreesC and 37degreesC but was stable at 4degreesC and --20degreesC for periods up to two weeks. The proportional increase in T4(CPB) and free fatty acids (FFA) indicated that this phenomenon was due, at least partly, to the interference from FFA formed during storage of the serum. There was also a small, significant increase in T3U, T3(RIA) and CT4I (a free thyroxine estimate) after storage of serum at room temperature or higher for one to two weeks. Serum T4(RIA) did not alter during two weeks of storage. In five subjects with raised serum FFA after eating a fat meal followed by a heparin injection an increase in T4(CPB), T3U, T3(RIA) and CT4I that was proportional to the increase in FFA was observed. This effect on the thyroid tests was small until the increase in FFA concentration exceeded 2 mmol/l. T4(RIA) did not respond to the increase in FFA. In ten patients with raised levels of FFA due to uncontrolled diabetes T4(CPB), T4(RIA) and T3(RIA) decreased while T3U increased. These unexpected alterations were probably related to the severe, chronic illness in these patients. Increased FFA in vivo seem to be of little importance for the interpretation of thyroid tests in clinical practice.

Hormonal changes in severely uncontrolled type 1 (insulin-dependent) diabetes mellitus

To investigate endocrinological changes associated with severely uncontrolled type 1 (insulin-dependent) diabetes mellitus 27 patients (19 men, eight women) with ketoacidosis or severe ketonuria (= group 1) were examined on admission and after recovery. For comparison 13 non-ketotic patients (seven men, six women), admitted for adjustment of treatment because of poor diabetic control (= group 2), and 20 healthy controls were studied. On admission, the serum testosterone levels in men were lower in group 1 (15.1 +/- 2.0 nmol l-1) (mean +/- SEM) than in group 2 (27.2 +/- 2.8 nmol l-1) (p less than 0.01) and healthy controls (20.6 +/- 2.0 nmol l-1) (p less than 0.05). During treatment the testosterone levels in group 1 rapidly rose to the control level. The serum oestradiol levels in women were low in group 1 both on admission and discharge. The serum prolactin levels were low in female patients in group 1 (119 +/- 17 mIU l-1) compared with the women in group 2 (315 +/- 75 mIU l-1) (p less than 0.05). On admission the serum cortisol levels were higher and their response to 1 mg of dexamethasone was weaker in group 1 than in group 2 and healthy controls. After recovery the serum cortisol levels fell by 15% (p less than 0.01) and the response to 1 mg of dexamethasone returned to normal in group 1. In group 1 during treatment the serum free T4 and reverse T3 levels fell, and the T3 levels rose, whereas the thyroid stimulating hormone (TSH) levels and their responses to TRH remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Five guaiac-based tests for occult blood in faeces compared in vitro and in vivo

Five guaiac-based faecal occult blood tests (Fecatest, Fecatwin Sensitive, Fecatwin, Haemoccult, Hemafecia) were compared in vitro and in vivo and the effect of time between sample application and development of the colour reaction was studied. In both type of experiments the sensitivity of Fecatest, Fecatwin Sensitive and Fecatwin was higher when the colour reaction was developed at 24-72 h than at 2 h after application of the sample but for Haemoccult and Hemafecia the sensitivity in in vivo experiments was constant or tended to decrease with time. In upper gastrointestinal bleeding false negative test results were obtained for Fecatest, Fecatwin Sensitive, Fecatwin, Haemoccult and Hemafecia in 21, 23, 38, 43 and 43%, respectively. In colorectal bleeding the corresponding percentages were 10, 10, 35, 35 and 35. Using the 51Cr-erythrocyte method, quantitative estimation of intestinal bleeding was performed in 20 patients with verified colorectal cancer and in 11 control patients. When the patient was bleeding from left hemicolon 29% of the Fecatwin, Haemoccult and Hemafecia test results were negative, 10% were negative for Fecatest and 14% for Fecatwin Sensitive. In patients with tumours in right hemicolon Fecatest and Fecatwin Sensitive were positive in all samples, whereas the other tests were negative in 10%. Experiments revealed that the proportion of false positives due to dietary factors correlated with the sensitivity of the tests.

ASSESSMENT OF THYROXINE SUPPRESSION IN THYROID CARCINOMA PATIENTS WITH A SENSITIVE IMMUNORADIOMETRIC TSH ASSAY

Serum TSH was determined with a sensitive radioimmunometric method (TSH IRMA) in 57 patients on suppression therapy with T4 after operation for differentiated thyroid carcinoma. When using a conventional RIA technique basal TSH was not detectable and remained so even after stimulation with TRH. With the TSH IRMA method 46 patients had a basal TSH below the detection limit (0·02 mU/l) (81 %) and in seven patients the values were between 0·02 and 0·05 mU/l (12%). In 23 of these patients there was a small increment of 0·01–0·15 mU/l. In two patients the basal TSH was 0·08 and 0·09 mU/l, and the increment after TRH was less than 0·7 mU/l. In two other patients with basal values close to 0·2 mU/l the increment after TRH was more than 1·0 mU/l. An undetectable basal TSH value did not thus predict an absent response to TRH. The responses were, however, in all but two cases, so small that they could be regarded as clinically insignificant. Therefore, the authors conclude that a basal TSH of 0·1 mU/l, as measured with a TSH IRMA method with a detection limit of 0·05, is a sufficient indication of TSH suppression in carcinoma patients on T4 therapy and that further testing with the TRH‐stimulation test is unnecessary.

Assessment of thyroid status by laboratory methods: Developments and perspectives

Serum protein-bound iodine and in vivo radioiodine tests were employed for over three decades although their usefulness was hampered by interference from iodinated compounds. Tests reflecting thyroid hormone action were therefore used for additional information on thyroid status. Competitive saturation analysis of serum T4 was introduced in the 60s. RIAs for T4 and T3 were not developed until ten years later because of problems in raising polyclonal antibodies to small haptens. Methods for FT4 and FT3 based on equilibrium dialysis of serum labelled with radioiodinated hormone emerged in the 60s, and in the 70s sensitive RIAs enabled direct determination of free hormone concentrations in serum dialysate. Dialysis and ultrafiltration methods are tedious and therefore various free hormone indices, based on total hormone concentrations and tests for unoccupied thyroid hormone-binding sites, have been used right up to our times. In the 80s rapid assays for FT4 and FT3 based on varying principles were developed particularly by commercial companies. Free hormone assays utilizing thyroid hormone analogs as tracers have been criticized because binding of analogs to serum proteins results in spurious values in conditions characterized by thyroid hormone-binding protein abnormalities. Bioassay of TSH was not adopted by the clinical service laboratory because of insufficient analytical sensitivity. The first immunological TSH assay, based on cross-reaction of human and bovine TSH in a hemagglutination inhibition test, was also too insensitive for practical purposes. RIAs for direct determination of normal TSH concentrations were developed in the 60s. The breakthrough in measurement of low TSH concentrations occurred in the 80s with the advent of immunometric assays utilizing monoclonal antibodies. Recently chemiluminescence, fluorescence and enzyme labels have been used for the development of non-isotopic methods for thyroid hormones and TSH. Immunoassay systems for bed-side measurement of analyte concentrations are being developed and immunosensors for continuous monitoring of analyte levels will probably be available in the future.

Performance of direct equilibrium dialysis and analogue-type free thyroid hormone assays, and an immunoradiometric TSH method in patients with thyroid dysfunction

Direct equilibrium dialysis and analogue-type radio-immunoassays for free triiodothyronine (FT3) and free thyroxine (FT4) in serum were compared in 168 subjects with various states of thyroid function. A good diagnostic efficacy for FT3 and FT4 by either type of assay was observed in hyperthyroidism. In hypothyroidism the free thyroid hormone assays, particularly the FT3 assays, performed diagnostically less well, partly because patients with mild disease were included in the study. No significant differences in the percentages of misclassifications of thyroid dysfunction patients by corresponding dialysis and analogue assays were found. We observed a good linear correlation between dialysis and analogue methods for FT3 (r = 0.98) and FT4 (r = 0.97) in this study comprising out-patients not suffering from severe non-thyroidal disease, known from earlier studies in this and other laboratories to interfere in these assays. It is concluded that analogue assays may be used on out-patients in whom severe systemic diseases are less frequent than in hospitalized patients. There are, however, other limitations to the use of analogue assays than systemic diseases. We observed two euthyroid patients with thyroxine auto-antibodies causing very high FT4 concentrations as determined by analogue assay; their dialysable FT4 concentrations were normal. We also tested a recently developed immunoradiometric serum TSH assay, which was found to perform well in primary hypo- and hyperthyroidism. Serum TSH was elevated in one patient hyperthyroid because of a TSH-producing pituitary adenoma, and within the reference limits in a patient with secondary hypothyroidism.