The Experts below are selected from a list of 1344 Experts worldwide ranked by ideXlab platform
Samuel Refetoff - One of the best experts on this subject based on the ideXlab platform.
-
Free Thyroxine concentrations in sera of individuals with familial dysalbuminemic hyperThyroxinemia a comparison of three methods of measurement
Thyroid, 2020Co-Authors: Samuel Refetoff, Neal H Scherberg, Chao Yuan, Michael J McphaulAbstract:Background: Euthyroid individuals with familial dysalbuminemic hyperThyroxinemia (FDH) have often falsely elevated serum Free Thyroxine (fT4) concentrations determined by different automated immunoassays. Methods: We measured serum fT4 using direct dialysis coupled with tandem mass spectrometry (fT4 DDMS) in individuals with the common albumin gene mutation (ALB R218H) from 14 FDH families and compared them with results obtained by direct immunometric assay (fT4 DIMM) and Free Thyroxine Index (fT4I). Results: While all 14 individuals with FDH had elevated total serum T4, the fT4 measured by DIMM was elevated in 12, by fT4I in 5, and by DDMS in 1. Conclusion: The latter method greatly reduced the discordance of fT4 results relative to thyrotropin in FDH.
-
low serum Free Thyroxine Index in ambulating elderly is due to a resetting of the threshold of thyrotropin feedback suppression
The Journal of Clinical Endocrinology and Metabolism, 1991Co-Authors: G F Lewis, Cathy A Alessi, Jacqueline Imperial, Samuel RefetoffAbstract:Subnormal Free T4 Index (FT4I) values ( 90) and TSH levels. The former also had low serum total T4 (TT4) and rT3 (TrT3) concentrations, but total T3 (TT3) and basal TSH values were normal and did not differ between the groups. Responses of ACTH, LH, FSH, TSH, and PRL to stimulation with CRH, GnRH, and TRH showed no differences between the two groups, indicating that the normal TSH concentration, inappropriate for the low FT4I level, is not due to generalized hypothalamic or pituitary dysfunction. Administration of 3 g iopanoic acid (IOP) daily for 3 days produced significant increases in the TT4 and TrT3 concentrations to the same degree...
F R Velazquez - One of the best experts on this subject based on the ideXlab platform.
-
indirect estimation of thyroid hormone binding proteins to calculate Free Thyroxine Index comparison of nonisotopic methods that use labeled Thyroxine t uptake
Clinical Chemistry, 1995Co-Authors: James D Faix, H N Rosen, F R VelazquezAbstract:There are many alternative ways of estimating Free Thyroxine (T4) when thyrotropin screening results are abnormal. In addition to Free T4 immunoassays, the menu of most automated immunoassay instruments includes a nonisotopic version of the original triiodothyronine (T3)-uptake assay called "T-uptake." We evaluated the ability of five such assays (Access, ES-300, IMx, Magnum Opus, and Stratus) to accurately estimate the Free Thyroxine Index (FTI) in euthyroid, hyperthyroid, and hypothyroid patients with abnormal concentrations of thyroid hormone-binding proteins, and in patients with nonthyroidal illness. For comparison, we calculated a similar FTI, using either T3-uptake or direct measurement of Thyroxine-binding globulin (TBG). Euthyroid reference ranges were comparable. Of euthyroid patients with increased TBG, 12-32% and 5-20% had increased or suppressed FTI, respectively, depending on the T-uptake method used. Except for IMx, 6-35% of hypothyroid patients with increased TBG had inappropriately increased FTI. Patients with nonthyroidal illness had comparable results regardless of the method used, and T-uptake methods were variably affected by known inhibitors of thyroid hormone binding. The most reliable T-uptake method appeared to be the IMx, which, despite claims that it measures all thyroid hormone-binding proteins, correlated best with TBG concentrations.
James V Hennessey - One of the best experts on this subject based on the ideXlab platform.
-
use of the Free Thyroxine Index to refine the lower limit of a Free Thyroxine immunoassay for detection of secondary hypothyroidism
Endocrine Practice, 2021Co-Authors: Gregory P Westcott, Christopher M Mulla, James V HennesseyAbstract:Abstract Objective To determine the utility of measuring Free T4 Index (FT4I) in patients with low Free T4 (FT4) levels using immunoassay and normal thyroid-stimulating hormone for the evaluation of secondary hypothyroidism. Methods We performed a retrospective medical chart review of patients seen at a single institution as outpatients who had a simultaneously normal thyroid-stimulating hormone level, low FT4 level, and any FT4I measured between June 2014 and October 2016. Demographic, laboratory, and imaging data were collected. Using FT4I as the reference for diagnosis of hypothyroidism, the sensitivity and specificity of the FT4 immunoassay’s lower-limit thresholds were determined. Within each threshold group, available brain imaging and biochemical evaluation were categorized according to the presence or absence of pituitary disease. Results A total of 155 sets of result pairs (FT4 and FT4I) performed on 118 subjects were analyzed. The lower limit of a normal FT4 level by immunoassay at this institution was 0.93 ng/dL, though all pairs with FT4 ≥0.89 ng/dL had a normal FT4I. All pairs with FT4 ≤0.67 ng/dL had a low FT4I. No pituitary macroadenomas were identified in any subject, though the rates of pituitary imaging in this patient sample were low. Conclusion Patients with a borderline low FT4 level by immunoassay often have normal FT4I. In such patients at our center, significant structural and biochemical pituitary pathology was uncommon.
Michael J Mcphaul - One of the best experts on this subject based on the ideXlab platform.
-
Free Thyroxine concentrations in sera of individuals with familial dysalbuminemic hyperThyroxinemia a comparison of three methods of measurement
Thyroid, 2020Co-Authors: Samuel Refetoff, Neal H Scherberg, Chao Yuan, Michael J McphaulAbstract:Background: Euthyroid individuals with familial dysalbuminemic hyperThyroxinemia (FDH) have often falsely elevated serum Free Thyroxine (fT4) concentrations determined by different automated immunoassays. Methods: We measured serum fT4 using direct dialysis coupled with tandem mass spectrometry (fT4 DDMS) in individuals with the common albumin gene mutation (ALB R218H) from 14 FDH families and compared them with results obtained by direct immunometric assay (fT4 DIMM) and Free Thyroxine Index (fT4I). Results: While all 14 individuals with FDH had elevated total serum T4, the fT4 measured by DIMM was elevated in 12, by fT4I in 5, and by DDMS in 1. Conclusion: The latter method greatly reduced the discordance of fT4 results relative to thyrotropin in FDH.
Christopher M Mulla - One of the best experts on this subject based on the ideXlab platform.
-
use of the Free Thyroxine Index to refine the lower limit of a Free Thyroxine immunoassay for detection of secondary hypothyroidism
Endocrine Practice, 2021Co-Authors: Gregory P Westcott, Christopher M Mulla, James V HennesseyAbstract:Abstract Objective To determine the utility of measuring Free T4 Index (FT4I) in patients with low Free T4 (FT4) levels using immunoassay and normal thyroid-stimulating hormone for the evaluation of secondary hypothyroidism. Methods We performed a retrospective medical chart review of patients seen at a single institution as outpatients who had a simultaneously normal thyroid-stimulating hormone level, low FT4 level, and any FT4I measured between June 2014 and October 2016. Demographic, laboratory, and imaging data were collected. Using FT4I as the reference for diagnosis of hypothyroidism, the sensitivity and specificity of the FT4 immunoassay’s lower-limit thresholds were determined. Within each threshold group, available brain imaging and biochemical evaluation were categorized according to the presence or absence of pituitary disease. Results A total of 155 sets of result pairs (FT4 and FT4I) performed on 118 subjects were analyzed. The lower limit of a normal FT4 level by immunoassay at this institution was 0.93 ng/dL, though all pairs with FT4 ≥0.89 ng/dL had a normal FT4I. All pairs with FT4 ≤0.67 ng/dL had a low FT4I. No pituitary macroadenomas were identified in any subject, though the rates of pituitary imaging in this patient sample were low. Conclusion Patients with a borderline low FT4 level by immunoassay often have normal FT4I. In such patients at our center, significant structural and biochemical pituitary pathology was uncommon.
