8
Table 6. Causes of Artifactual Results in Thyroid Hormone Assays
Assay Interference Analyte Effect
Immunoassay Antireagent antibodies, Assay specific:
Antianimal Ig
Biotin/streptavidin
Ruthenium heterophile antibodies
TSH
Blocking
Crosslinking
f T4
Blocking
Anti-hormone autoantibodies ''macro
TSH''
b
TSH
Anti-T4 antibodies f T4
Genetic variation in TSH p.(Arg75Gly)
25950606
TSH
T4 binding protein abnormalities
Familial Dysalbuminemic
Hyperthyroxinemia (FDH),
Dystransthyretinemic hyperthyroxinemia
(DTH)
f T4
f T4 TT4
Free T4 assay
(direct and
indirect assay)
Displacing agents
In vitro free fatty acid generation by heparin
Re-equilibration of T4 during assay
f T4
f T4
f T4 TT4⇋
f T4
a
Polyethylene glycol (PEG).
b
Data from study of 1794 women of reproductive age @ heterozygotes have intermediate results.
c
Anti-T4 antibodies are frequently detected, however, relatively few cases are associated with assay
interference that is typically only seen with one-step methods.
d
Autosomal dominant conditions.
