The T₄:TBG Ratio: A Re-Evaluation with Particular Reference to Low and High Serum TBG Levels

Abstract

SUMMARYThe thyroxine: thyroxine-binding globulin (T,,: TBG) ratio is now an established part of the biochemical investigation of thyroid function. Reference ranges have been reported for euthyroid subjects with TBG levels within the range 6--16 mg/l. Routine assay ofTBG on all thyroid function tests in this laboratory has suggested that, in patients with low or high TBG levels, the established reference ranges for T,: TBG may not be strictly applicable.A retrospective study has been made of a large number of thyroid function requests, including serum total T" free T" TBG, and TSH assays. Evidence is presented to show that in subjects with a TBG level of less than 8 mg/l the reference range for T,: TBG is elevated. Similarly, in subjects with a TBG greater than 16 mg/l, the reference range for T,: TBG is lowered. The data suggest that it is necessary to quote aT,: TBG reference range based on small increments of TBG levels or to relate total T, reference ranges to those increments.

Interpretation of in‐vitro thyroid function tests during pregnancy

“…The commonly used laboratory index of free T,. the T,/TBG ratio, appears significantly to underestimate free T, levels in pregnancy, and Attwood & Atkin (1982) have also shown this effect in subjects with high TBG levels who are not pregnant. Hypothyroid T,/TBG ratio values were obtained in the third trimester but raised TSK levels were not found.…”

Higher Thyroid-Stimulating Hormone, Triiodothyronine and Thyroxine Values Are Associated with Better Outcome in Acute Liver Failure

“…Reduction of total but not free hormone concentrations in NSR compared to SR patients might imply a deficit of transport proteins produced by the liver (i.e. thyroid hormone-binding globulin (TBG) or albumin), which are crucial for thyroid hormone function [ 36 ]. This has been described in patients receiving bypass surgery, where TBG levels diminished rapidly after surgery [ 37 ].…”

Akut Karaci̇ğer Yetmezli̇ği̇ Olan Çocuklarda Ti̇roi̇d Hormonlarinin Ve Hastaliğin Seyri̇ İle İli̇şki̇si̇ni̇n Değerlendi̇ri̇lmesi̇

“…Ölçüm tekniklerine göre farklılık göstermekle birlikte, hastalık durumundaki sT3 ve sT4 düzeyleri, genellikle total T3 ve total T4 düzeyleri gibi azalmakta, fakat bu düşüş daha hafif düzeyde kalmaktadır (8,16). Total tiroid hormonlarındaki düşmenin serbest tiroid hormonlarına göre daha fazla olmasının nedeninin, hastalık sırasında akut faz cevabı olarak tiroid bağlayıcı proteinlerin azalması olduğu düşünülmektedir (8,18,19…”