Serum free 3,5,3'-triiodothyronine (T3) in non-thyroidal somatic illness, as measured by ultrafiltration and immunoextraction.
Serum free 3,5,3'-triidothyronine (T3) levels are regularly reported reduced in patients with non-thyroidal, somatic illnesses (NTI). However most free T3 assays have serious methodologically shortcoming. From a theoretical point of view, ultrafiltration may be the most reliable technique at present, and we have previously reported unaltered serum free T3 levels in NTI. A newly commercialized assay suitable for routine use (Amerlite MAB free T3) has demonstrated promising results in NTI sera, and we thus compared these two methods in a large group of NTI patients not treated with glucocorticoids or dopamine (n = 120), as well as in 66 healthy controls and 8 patients on prolonged dopamine infusion. In both assays free T3 levels were unaltered in NTI (NTI versus controls (mean), Amerlite MAB free T3: 5.47 versus 5.32 pmol/l; ultrafiltration 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 and 2% using the ultrafiltration assay. The two methods correlated in all subjects (n = 194) (r = 0.32 (P < 0.001) as well as in NTI patients (r = 0.34 (P < 0.001). No correlations to serum T4 levels were found, and patients with serum T4 levels below or above 70 nmol/l, had similar free T3 concentrations in both assays. Patients on dopamine infusion had reduced serum free T3 levels (both assays), but the values were still within the normal range.


CONCLUSIONS
Serum free T3 levels were unaltered in NTI patients using both assays, and the Amerlite MAB free T3 assays seems useable during diagnostic work-up for possible thyroid disease in hospitalized patients with other somatic illnesses, despite the fact that this assay has some shortcomings, which are an integral part of all immunoextraction assays.
Faber
J
J
Department of Endocrinology E, Frederiksberg Hospital, Denmark.
Siersbaek-Nielsen
K
K
D006801:Humans; D007159:Immunologic Tests; D011933:Reagent Kits, Diagnostic; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood*; D014462:Ultrafiltration
D011933:Reagent Kits, Diagnostic; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine