Semi-automated radioimmunoassays for total serum thyroxine and triiodothyronine

Baird

1977

Brit J Clinical Pharma

Section: Effect Of IV Heparin On Serum Free Triiodothyronine Levelsmentioning

confidence: 99%

Effect of I.V. Heparin on Serum Free Triiodothyronine Levels

Baird

1977

Brit J Clinical Pharma

“…T4 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).…”

Section: Methodsmentioning

confidence: 99%

Thyroid Function Tests in Thyroxine-Binding Globulin Deficiency

Cusick

1979

Ann Clin Biochem

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.

“…The adsorbed hormone is eluted from the silica at a different pH, and the eluant is subjected to normal CPB methodology. The routine method of T4 estimation in our other laboratory is a semi-automated radioimmunoassay using a second antibody separation (Challand et al, 1975). In routine use the interassay and intra-assay coefficients of variation are 7'7% and 3'5% respectively, with a laboratory normal range of 55-144 nmoi/i.…”

Section: Estimation Of Serum Thyroxinementioning

confidence: 99%

Discrepancies in Thyroxine Measurement in Pregnancy between Radioimmunoassay and Competitive Protein Binding (Oxford StaT₄)

Baird

et al. 1978

Ann Clin Biochem

Summary The StaT4 test is a technically simple test of thyroxine measurement, which apparently gives results in good agreement with those derived by radioimmunoassay in most patients. In pregnancy, however, falsely low serum thyroxine values were found with the StaT4 test when compared with either a radioimmunoassay or the Thyopac-4 test. Detailed studies showed that the discrepancy resulted from the extraction technique used in the StaT4 test, which appears to allow the patient's thyroxine binding proteins to remain in the assay system. Similar method discrepancies were observed in other clinical conditions associated with elevated thyroxine binding globulin concentration. This study, as well as being of practical clinical importance, has implications for the design of competitive protein binding tests of thyroid function.