Clinical Application of Serum-Total-Thyroxine Estimation, Resin Uptake, and Free-Thyroxine Index

Howorth, P. J. N.; Maclagan, N. F.

doi:10.1016/s0140-6736(69)91240-9

Cited by 62 publications

(21 citation statements)

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“…The derived index, FIT, was initially reported to compensate for abnormal levels of the thyroxine-binding proteins (Howorth and MacLagen, 1969), but it has become increasingly recognised that this is not always correct, and reliance on this index may lead to a false diagnosis of thyroid status (Premachandra et al, 1976). A direct assay of thyroxine binding globulin (TBG) in serum was first described by Freeman and Pearson in 1969, soon followed by the first radioimmunoassay (Levy et al, 1970).…”

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confidence: 99%

An Evaluation of Serum Thyroxine Binding Globulin as a Routine Test of Thyroid Function

McDowell

1979

Ann Clin Biochem

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SUMMARY Serum thyroxine binding globulin (TBG) values were correlated with other thyroid function test results and with the clinical condition in 680 patients. The estimation of serum TBG was helpful in the evaluation of thyroid status only in those patients who were either acutely ill, were taking the contraceptive pill, or were pregnant. Further, the derived index, thyroxine: TBG ratio, proved to be a better diagnostic index than the thyroxine: tri-iodothyronine uptake ratio and in many cases would have avoided the use of more expensive and time-consuming tests.The assays commonly used to detect thyroid dysfunction are a combination of serum thyroxine (T4), tri-iodothyronine uptake (T3-uptake), and free thyroxine index (FT!) as first-line tests, with serum T3, thyroid stimulating hormone (TSH), and the thyrotrophin releasing hormone (TRH) stimulation test to augment the diagnosis. With these tests it is possible to confirm the thyroid status of the majority of patients (Pain and Duncan, 1976;Evered et al., 1978).In a proportion of patients, especially those who are on antidepressant therapy, are taking the contraceptive pill, are pregnant, have severe nonthyroidal disease, or are elderly, the above tests become more difficult to interpret because of abnormal levels of the thyroid hormone binding proteins (Oppenheimer, 1968). The derived index, FIT, was initially reported to compensate for abnormal levels of the thyroxine-binding proteins (Howorth and MacLagen, 1969), but it has become increasingly recognised that this is not always correct, and reliance on this index may lead to a false diagnosis of thyroid status (Premachandra et al., 1976). A direct assay of thyroxine binding globulin (TBG) in serum was first described by Freeman and Pearson in 1969, soon followed by the first radioimmunoassay (Levy et al., 1970). It was the purpose of this study to investigate the relationships of TBG to the other thyroid parameters and to ascertain whether its routine use aids the differentiation of the thyroid disorders. Patients and methodsThyroid status was determined using assays of serum 'Present address: Department of Chemical Pathology, Hope Hospital, Eccles Old Road, Salford M6 8HD T4, T 3-uptake, and FT!, followed by assays of serum T3, TSH, or a TRH-stimulation test where appropriate. Details of age, sex, therapy, and clinical diagnosis were recorded at the same time. The patients were then classified as follows:1 Acutely ill: patients having severe non-thyroidal diseases (eg, congestive cardiac failure, myocardial infarction, severe diabetes, carcinoma, renal failure).2 Contraceptive pill users: women between the ages of 16 and 40 years who are currently taking any form of oral contraceptive (for periods greater than six months).3 Pregnant: women between the ages of 16 and 40 years and at between 20 and 40 weeks' of pregnancy.4 Borderline hypothyroid: patients having either one result in the hypothyroid range or all results outside 75 % of normal limits.5 Hypothyroid: patients having all results in the hypothyro...

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An Evaluation of Serum Thyroxine Binding Globulin as a Routine Test of Thyroid Function

McDowell

1979

Ann Clin Biochem

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“…Thus the euthyroid woman who is found to have a raised concentration of serum T.B.G. as a consequence of pregnancy or oestrogen medication (most often as a contraceptive) often shows a T-4 concentration that is raised above normal (Murphy et al, 1966;Howorth and Maclagan, 1969). Although other causes of both increased and decreased concentrations of T.B.G.…”

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confidence: 99%

“…However, currently accepted dialysis and ultrafiltration techniques used to measure directly serum-free T-4 are too cumbersome to have clinical application (Oppenheimer, 1968). Similarly the calculation of a free T-4 index or free T-4 factor from serum T-4 (or proteinbound iodine) and the resin uptake of either T-4 or triiodothyronine (T-3) (Clark and Horn, 1965;Goolden et al, 1967;Howorth and Maclagan, 1969), though correlating well with thyroid status in the presence of a binding protein abnormality, is cumbersome in that two separate procedures involving many steps are required for the calculation.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a New In-vitro Blood Test for Determining Thyroid Status: The Effective Thyroxine Ratio

Thorson¹,

Mincey²,

McIntosh³

et al. 1972

BMJ

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“…While thyroid hormone uptake tests or TBG assay were effective in the recognition of such individuals, indices based on these tests were misleading in assessing their thyroid status. Results within the reference range were obtained with the Immophase Free Thyroxine assay.More than 99 % of circulating thyroxine is protein bound, but it is the small free thyroxine concentration (free-T4) that determines thyroid status (Ingbar and Freinkel, 1960).The serum total thyroxine (T4) concentration has been used to measure thyroid function, although it changes independently of thyroid activity when the concentration of binding protein is altered.Attempts to compensate for binding abnormalities include the free-thyroxine index (FTI) (Howorth and MacLagen, 1969) and T4: TBG ratio (Burr et al, (1977), in both of which the T4 concentration is divided by a measure of binding protein levels. The Immophase Free-T4 kit (Corning Medical, Halstead) gives absolute free-T4 results by a rate method.…”

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confidence: 99%

“…Attempts to compensate for binding abnormalities include the free-thyroxine index (FTI) (Howorth and MacLagen, 1969) and T4: TBG ratio (Burr et al, (1977), in both of which the T4 concentration is divided by a measure of binding protein levels. The Immophase Free-T4 kit (Corning Medical, Halstead) gives absolute free-T4 results by a rate method.…”

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confidence: 99%

Thyroid Function Tests in Thyroxine-Binding Globulin Deficiency

Cusick

1979

Ann Clin Biochem

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SUMMARY Results are presented on two patients with complete and two with partial thyroxinebinding globulin (TBG) deficiency. All four subjects had lowered serum thyroxine but were clinically euthyroid. While thyroid hormone uptake tests or TBG assay were effective in the recognition of such individuals, indices based on these tests were misleading in assessing their thyroid status. Results within the reference range were obtained with the Immophase Free Thyroxine assay.More than 99 % of circulating thyroxine is protein bound, but it is the small free thyroxine concentration (free-T4) that determines thyroid status (Ingbar and Freinkel, 1960).The serum total thyroxine (T4) concentration has been used to measure thyroid function, although it changes independently of thyroid activity when the concentration of binding protein is altered.Attempts to compensate for binding abnormalities include the free-thyroxine index (FTI) (Howorth and MacLagen, 1969) and T4: TBG ratio (Burr et al., (1977), in both of which the T4 concentration is divided by a measure of binding protein levels. The Immophase Free-T4 kit (Corning Medical, Halstead) gives absolute free-T4 results by a rate method.In the present paper, these three approaches are compared in four patients with very low or undetectable TBG concentrations. MethodsT4 and serum triiodothyronine (T3) (Challand et al., 1975) and thyrotropin (TSH) (Burrin, 1976) were measured by radioimmunoassay, while TBG was determined by rocket immunoelectrophoresis (Bradwell et al., 1976).Commercial kits were used for the serum thyroid hormone uptake (Thyopac-3) (Radiochemical Centre Amersham) and Immophase Free T4. FTI = (T4 x 1(0) --:-Thyopac-3, and T4 : TBG ratio were both calculated.

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Clinical Application of Serum-Total-Thyroxine Estimation, Resin Uptake, and Free-Thyroxine Index

Cited by 62 publications

References 17 publications

An Evaluation of Serum Thyroxine Binding Globulin as a Routine Test of Thyroid Function

An Evaluation of Serum Thyroxine Binding Globulin as a Routine Test of Thyroid Function

Evaluation of a New In-vitro Blood Test for Determining Thyroid Status: The Effective Thyroxine Ratio

Thyroid Function Tests in Thyroxine-Binding Globulin Deficiency

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