Establishment of the Trimester-Specific Reference Range for Free Thyroxine Index

Thyroid ◽  
2013 ◽  
Vol 23 (3) ◽  
pp. 354-359 ◽  
Author(s):  
Fereidoun Azizi ◽  
Ladan Mehran ◽  
Atieh Amouzegar ◽  
Hossein Delshad ◽  
Maryam Tohidi ◽  
...  
Keyword(s):  
Reference Range ◽  
Free Thyroxine ◽  
Specific Reference ◽  
Free Thyroxine Index

Effects of Age and Health on the Euthyroid Reference Ranges for Serum Free Thyroxine and Free Triiodothyronine

1985 ◽  
Vol 24 (02) ◽  
pp. 57-65 ◽  
Author(s):  
J. E. M. Midgley ◽  
K. R. Gruner
Keyword(s):  
Lower Limit ◽  
Healthy Subjects ◽  
Thyroid Dysfunction ◽  
Reference Range ◽  
Free Thyroxine ◽  
Reference Ranges ◽  
Free Triiodothyronine ◽  
Serum Free ◽  
Young Subjects ◽  
Age Range

SummaryAge-related trends in serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations were measured in 7248 euthyroid subjects (age-range 3 months to 106 years). 5700 were patients referred to hospitals for investigation of suspected thyroid dysfunction, but who were diagnosed euthyroid. 1548 were healthy blood donors (age-range 18-63 years) with no indication of thyroid dysfunction. FT4 concentrations were little affected by the age, the sex or the state of health of the subjects in either group. Serum FT3 concentrations were significantly affected by both age and health factors. The upper limit of the euthyroid reference range for young subjects up to 15 years was about 20% higher (10.4 pmol/1) than for adult subjects older than 25 years (8.8 pmol/1). The change in the upper limits typical of young subjects to that typical of adults occurred steadily over the decade 15–25 years. After this age, little further change occurred, especially in healthy subjects. Additionally, the lower limit of the euthyroid range for FT3 was extended by the inclusion in the reference group of patients referred to hospitals. Compared with the lower limit of the FT3 range for healthy subjects (5 pmol/1), the corresponding limit for referred subjects (young or adult) was 3.5–3.8 pmol/1. Broadening of the FT3 reference range was probably brought about by a significant number of patients in the hospital-referred group with the “1OW-T3 syndrome” of mild non-thyroidal illness. Accordingly, FT3 was inferior to FT4 in the discrimination of hypothyroidism, as FT4 was unaffected by this phenomenon. Effects of age and non-thyroidal illness on serum FT3 concentrations require great care when selecting subjects for a laboratory euthyroid reference range typical of the routine workload. Constraints on the choice of subjects for FT4 reference ranges are less stringent.

A Comparison of Serum Thyroxine [T4(D)], RT3U Ratio and T4-RT3 Index with Radioiodine Uptake in the Triiodothyronine Suppression Test

1972 ◽  
Vol 11 (04) ◽  
pp. 317-323
Author(s):  
R. Höschl ◽  
T. M. D. Gimlette
Keyword(s):  
Free Thyroxine ◽  
Radioiodine Uptake ◽  
Serum Thyroxine ◽  
Before And After ◽  
Free Thyroxine Index ◽  
Suppression Test

SummaryA total of 132 triiodothyronine suppression tests were performed using 100 μg of T3 for 7 days. Radioiodine uptake at four hours, serum thyroxine [T4(D)], T3 binding coefficient [RT3U ratio] and free thyroxine index [T4-RT3 index] were estimated before and after a course of triiodothyronine.T4(D) decreased significantly in only 38.4% of T3 suppression tests assessed as positive by the decrease in radioiodine uptake; it did not change or increased significantly in 84.7% of tests negative by radioiodine uptake.RT3U ratio showed little change in all groups. The changes in T4-RT3 index were similar to those of T4(D).The correlation of changes in T4(D) with 4 hour radioiodine uptake is poor (r = 0.34).Agreement between changes in radioiodine uptake and T4(D) was observed only in 54% of tests; between changes in uptake and T4-RT3 index in 69.4%.Estimation of serum thyroxine or free thyroxine index in the T3 suppression test cannot substitute for the radioiodine uptake for reasons which are discussed.

Evaluation of Thyroid Function in Pregnant Women Using Automated Immunoassays

2021 ◽  
Author(s):  
K Aaron Geno ◽  
Matthew S Reed ◽  
Mark A Cervinski ◽  
Robert D Nerenz
Keyword(s):  
Pregnant Women ◽  
Equilibrium Dialysis ◽  
Reference Interval ◽  
First Trimester ◽  
Reference Intervals ◽  
Free Thyroxine ◽  
Specific Reference ◽  
Childbearing Age ◽  
Thyroid Autoantibody ◽  
The Impact

Abstract Introduction Automated free thyroxine (FT4) immunoassays are widely available, but professional guidelines discourage their use in pregnant women due to theoretical under-recoveries attributed to increased thyroid hormone binding capacity and instead advocate the use of total T4 (TT4) or free thyroxine index (FTI). The impact of this recommendation on the classification of thyroid status in apparently euthyroid pregnant patients was evaluated. Methods After excluding specimens with thyroid autoantibody concentrations above reference limits, thyroid-stimulating hormone (TSH), FT4, TT4, and T-uptake were measured on the Roche Cobas® platform in remnant clinical specimens from at least 147 nonpregnant women of childbearing age and pregnant women at each trimester. Split-sample comparisons of FT4 as measured by the Cobas and equilibrium dialysis were performed. Results FT4 decreased with advancing gestational age by both immunoassay and equilibrium dialysis. TSH declined during the first trimester, remained constant in the second, and increased throughout the third, peaking just before delivery. Interpretation of TT4 concentrations using 1.5-times the nonpregnant reference interval classified 13.6% of first trimester specimens below the lower reference limit despite TSH concentrations within trimester-specific reference intervals. Five FTI results from 480 pregnant individuals (about 1.0%) fell outside the manufacturer’s reference interval. Conclusions Indirect FT4 immunoassay results interpreted in the context of trimester-specific reference intervals provide a practical and viable alternative to TT4 or FTI. Declining FT4 and increasing TSH concentrations near term suggest that declining FT4 is not an analytical artifact but represents a true physiological change in preparation for labor and delivery.

Free-thyroxine index in mania and depression

1978 ◽  
Vol 19 (6) ◽  
pp. 561-564 ◽  
Author(s):  
Pantelis Rinieris ◽  
George N. Christodoulou ◽  
Athanasius Souvatzoglou ◽  
Demetrios A. Koutras ◽  
Costas Stefanis
Keyword(s):  
Free Thyroxine ◽  
Free Thyroxine Index

Free-thyroxine index in psychotic and neurotic depression

1978 ◽  
Vol 58 (1) ◽  
pp. 56-60 ◽  
Author(s):  
P. M. Rinteris ◽  
G. N. Christodoulou ◽  
A. M. Souvatzoglou ◽  
D. A. Koutras ◽  
C. N. Stefanis
Keyword(s):  
Free Thyroxine ◽  
Free Thyroxine Index

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

1993 ◽  
Vol 39 (8) ◽  
pp. 1668-1674 ◽  
Author(s):  
R Docter ◽  
H van Toor ◽  
E P Krenning ◽  
M de Jong ◽  
G Hennemann
Keyword(s):  
Blood Donors ◽  
Reference Range ◽  
Equilibrium Dialysis ◽  
Free Thyroxine ◽  
Serum Samples ◽  
Nonthyroidal Illness ◽  
Nonesterified Fatty Acids ◽  
Thyroxine Binding Globulin ◽  
Control Value ◽  
The Mean

Abstract 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.

scholarly journals Pregnancy Week-Specific Reference Ranges for Thyrotropin and Free Thyroxine in the North Denmark Region Pregnancy Cohort

Thyroid ◽  
2019 ◽  
Vol 29 (3) ◽  
pp. 430-438 ◽  
Author(s):  
Stine Linding Andersen ◽  
Stig Andersen ◽  
Allan Carlé ◽  
Peter Astrup Christensen ◽  
Aase Handberg ◽  
...  
Keyword(s):  
Free Thyroxine ◽  
Specific Reference ◽  
Reference Ranges ◽  
Pregnancy Cohort ◽  
The North
Sign in / Sign up

Export Citation Format

Share Document