BACKGROUND: Three adult patients presented with unexpectedly high thyrotropin (TSH) concentrations that were discordant with clinical and biochemical findings of euthyroid or hyperthyroid status. METHODS: 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). RESULTS: 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. CONCLUSIONS: Interference by TSH-immunoglobulin complexes should be ruled out in euthyroid and hyperthyroid patients presenting with inappropriately increased or non-suppressed TSH values.
BACKGROUND: Three adult patients presented with unexpectedly high thyrotropin (TSH) concentrations that were discordant with clinical and biochemical findings of euthyroid or hyperthyroid status. METHODS: 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). RESULTS: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. CONCLUSIONS: Interference by TSH-immunoglobulin complexes should be ruled out in euthyroid and hyperthyroidpatients presenting with inappropriately increased or non-suppressed TSH values.