Proposed mechanisms whereby the T3U, dialyzed fraction (%FT4) and antibody extracted (AE) T4 normalize binding protein effects in free T4 (FT4) assays do not explain the findings in monthyroidally ill (NTI) patients

Conference · Sun Jan 01 00:00:00 EST 1984 · J. Nucl. Med.; (United States)

OSTI ID:6593737

Witherspoon, L R; Shuler, S E; Gilbert, S

Apparently falsely low FT4 results are observed in patients with NTI. FT4 estimates in NTI using some AE assays are lower than corresponding FTI. Both are lower than equilibrium dialysis (ED) results. These three approaches to FT4 estimation are similar - the T3U, %FT4 and %AE all are inversely related to TBG concentration. A FT4 estimate may be obtained by multiplying any of these x total T4 concentration. The mass of AE T4 may be quantitated by competitive binding, either after separation of AE T4 from serum (two step) or by employing a radiolabeled T4 analog recognized by the antibody but not by TBG. The authors made FT4 estimates in euthyroid patients with high, normal or low TBG concentrations; in hyper- and hypothyroid patients; and in NTI patients presumed euthyroid. Each approach produces similar results in euthyroid patients. The T3U and some AE assays display TBG dependence at TBG <10 and>50 ..mu..g/ml. In hyperthyroidism, the T3U is high, %FT4 normal or high, while the %AE is low. All FT4 results are high in hyperthyroidism. In hypothyroidism the T3U is low, %FT4 normal or low, while the %AE is high. All FT4 results are low in hypothyroidism. In NTI, the T3U is appropriate for the TBG concentration, %FT4 is often high and %AE is low. Furthermore, methods for quantifying the AE mass do not agree - index results are low, analog results lowers, such that %B/B is>100%, while the two step results are normal. The suggestion that the T3U, %FT4 and %AE all serve to normalize TBG effects in FT4 assays is inadequate. AE assays should be employed clinically with caution until the apparent anomalies, especially those seen in the analog systems, are explained.

• Research Organization: Ochsner Clinic, New Orleans, LA
• OSTI ID: 6593737
• Report Number(s): CONF-840619-; TRN: 87-018768
• Journal Information: J. Nucl. Med.; (United States), Vol. 25:5; Conference: 31. annual meeting of the Society of Nuclear Medicine, Los Angeles, CA, USA, 5 Jun 1984
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ENDOCRINE DISEASES
DIAGNOSIS
THYROID
BIOCHEMISTRY
DIAGNOSTIC TECHNIQUES
METABOLISM
ANTIBODIES
BIOASSAY
BIOCHEMICAL REACTION KINETICS
EVALUATION
HYPERTHYROIDISM
HYPOTHYROIDISM
LABELLING
PROTEINS
QUANTITATIVE CHEMICAL ANALYSIS
RADIOPHARMACEUTICALS
THYROID HORMONES
TISSUE DISTRIBUTION
UPTAKE
BODY
CHEMICAL ANALYSIS
CHEMISTRY
DISEASES
DISTRIBUTION
DRUGS
ENDOCRINE GLANDS
GLANDS
HORMONES
KINETICS
LABELLED COMPOUNDS
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HORMONES
REACTION KINETICS
550501* - Metabolism- Tracer Techniques