T4 Binding Proteins 36738X

Clinical Use Clinical Background • Evaluate patients with euthyroid Thyroid hormones normally circulate hyperthyroxinemia and hypo- bound to 1 of 3 classes of plasma thyroxinemic states proteins: thyroxine-binding globulin (TBG), transthyretin (prealbumin, Reference Range preALB), or albumin (see Test See next page Application and Interpretation section). Alterations in T4-binding Interpretive Information affinity and/or concentrations of these Mass of T4 bound to: proteins change the total and, in some TBG PreALB ALB cases, the free T4 concentrations. TBG deficiency ↓ NNThis thyroxine-binding protein panel TBG excess ↑ NNreveals the precise distribution of TBG variant ↓ NNprotein-bound T4 in plasma. TBPA excess N ↑ N Thyroxine-binding globulin excess, TBPA variants N ↑ N familial dysalbuminemic hyper- Dysalbuminemic NN↑ thyroxinemia (FDH), transthyretin- hyperthyroxinemia binding excess, and T4 antibodies can Euthyroid (sick) ↓↓N be differentiated. The panel can also hypothyroxinemia differentiate TBG deficiency and some molecular variants of TBG. Hypothyroidism ↓↓↓ Hyperthyroidism ↑↑↑Method Mass of T4 bound Quantify total T4 and binding proteins per unit mass of: • Immunochemiluminometric assay TBG PreALB ALB (total T4 and TBG) TBG deficiencyNNN• Fixed time nephelometry TBG excess NNN (prealbumin) TBG variant ↓ NN• Spectrophotometry (albumin) TBPA excessNNN TBPA variants N ↑ N Quantify T4 bound to each binding protein Dysalbuminemic NN↑ hyperthyroxinemia • Electrophoresis, radiobinding assay Euthyroid (sick) ↓↓N (TBG-, prealbumin-, albumin-bound hypothyroxinemia T4) Hypothyroidism ↓↓ ↓ Calculate T4 affinity of each binding Hyperthyroidism ↑↑↑protein • TBG-bound T4/TBG • Prealbumin-bound T4/prealbumin • Albumin-bound T4/albumin Specimen Requirements 4 mL refrigerated serum 2 mL minimum No additive red top preferred SST red top acceptable Continued

158 Alphabetical Test Section 36738X ) 159 continued ( μg/g μg/dL μg/mg μg/mL mg/dL 3700-5100 T4/prealbumin

3-8 y y9-13 y14-17 16.1-24.2 12.5-25.8 9.8-23.7 1st trimester trimester2nd trimester3rd All trimesters1-8 y y 6.4-15.2 9-13 7.4-15.2 y14-17 7.7-13.8 7.0-14.7 5.9-11.5 4.7-10.4 5.0-9.8 Adults y) (5-17 Children 0.5-1.0 0.5-1.2 Adults y) (5-17 Children 1.8-4.0 1.0-3.3 Adults y) (5-17 Children 2.6-5.8 2.1-6.2 MenWomenChildren MenWomen 13.5-30.9 12.7-25.1 17-34 21-43 Children AdultsPregnancy 4.8-10.4 Adults y) (5-17 Children 0.08-0.16 0.04-0.11 Adults y) (5-17 Children 2.0-3.0 Adults y) (5-17 Children 1.0-3.0 0.12-0.22 0.11-0.28 Reference Range Reference TBG Albumin-bound T4 Albumin-bound Prealbumin Prealbumin-bound T4 Prealbumin-bound Albumin TBG-bound T4 TBG-bound T4, Total T4, T4 Binding Proteins Proteins Binding T4 Albumin-bound T4/albumin T4/albumin Albumin-bound TBG-bound T4/TBG TBG-bound Prealbumin-bound