SERUM-FREE 3,5,3'-TRIIODOTHYRONINE (T3) IN NONTHYROIDAL SOMATIC ILLNESS, AS MEASURED BY ULTRAFILTRATION AND IMMUNOEXTRACTION

Serum free 3,5,3'-triiodothyronine (T3) levels are regularly reported reduced in patients with non-thyroidal, somatic illnesses (NTI). Howev er most free T3 assays have serious methodologically shortcomings. Fro m a theoretical point of view, ultrafiltration may be the most reliabl e technique at present, and we have previously reported unaltered seru m free T3 levels in NTI. A newly commercialized assay suitable for rou tine use (Amerlite MAB free T3) has demonstrated promising results in NTI sera, and we thus compared these two methods in a large group of N TI patients not treated with glucocorticoids or dopamine (n = 120), as well as in 66 healthy controls and 8 patients on prolonged dopamine i nfusion. In both assays free T3 levels were unaltered in NTI (NTI vers us controls (mean), Amerlite MAB free T3: 5.47 versus 5.32 pmol/l; ult rafiltration free T3: 6.99 versus 7.60 pmol/l). Free T3 levels outside normal range were found in 14% using the Amerlite MAB free T3 assay a nd 2% using the ultrafiltration assay. The two methods correlated in a ll subjects (n = 194) (r = 0.32 (P < 0.001)) as well as in NTI patient s (r = 0.34 (P < 0.001)). No correlations to serum T4 levels were foun d, and patients with serum T4 levels below or above 70 nmol/l, had sim ilar free T3 concentrations in both assays. Patients on dopamine infus ion had reduced serum free T3 levels (both assays), but the values wer e still within the normal range. Conclusion: Serum free T3 levels were unaltered in NTI patients using both assays, and the Amerlite MAB fre e T3 assay seems useable during diagnostic work-up for possible thyroi d disease in hospitalized patients with other somatic illnesses, despi te the fact that this assay has some shortcomings, which are an integr al part of all immunoextraction assays. Copyright (C) 1996 Elsevier Sc ience B.V.