Abstract
Results from a simple, fast and inexpensive Sephadex T3-uptake test (T3U) have been compared to free fractions of serum thyroxine (T4) and triiodothyronine (T3) determined by a dialysis procedure in forty-six sera from hypothyroids, 154 sera from euthyroids and ninety-one sera from hyperthyroids. Sera with high TBG levels were included in these groups. A second order correlation (r = 0.90) was found between T3U and free T4 and T3 fractions. The T3U had a low diagnostic value for all three groups. Free hormone indices calculated as the product between the T4 or T3 and T3U were linearly correlated to total free T4 (r = 0.94) and total free T3 (r = 0.96) if these are less than 2.5 times the upper normal level. It is concluded that the difficult and troublesome dialysis method for free hormone fractions can be replaced for practical clinical purposes by the T3U described.