Abstract
Three adult patients presented with unexpectedly high thyrotropin (TSH) concentrations that were discordant with clinical and biochemical findings of euthyroid or hyperthyroid status. Antibody interference in the TSH immunoassay (Roche) was investigated by polyethylene glycol (PEG)-pretreatment, heterophilic blocking tube (HBT)-pretreatment, rheumatoid factor (RF) testing, immunofixation, protein A adsorption, and gel filtration chromatography (GFC). PEG-precipitation yielded<20% recovery of serum TSH, whereas HBT-pretreatment did not decrease TSH test results. RF-testing and immunofixation were negative. Protein A adsorption and GFC demonstrated the presence of TSH-immunoglobulin complexes in serum. Interference by TSH-immunoglobulin complexes should be ruled out in euthyroid and hyperthyroid patients presenting with inappropriately increased or non-suppressed TSH values.
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