The TgR was compromised (<70%) in 91% of samples (10 of 11) that tested positive for TgAbs in both TgAb assays, whereas the TgR was within the reference interval ([greater than or equal to]70%) for 95% of samples that were negative for TgAbs in the TgAb-ICMA (96 of 101) and 97% of samples (98 of 101) that were negative in the TgAb-MEIA (Table 1B).
Ten of 12 (83%) sera with positivity for TgAbs in both assays had compromised TgR.
The detection of TgAbs in a patient means the loss of clinical utility of Tg measurements.
We also performed Tg-RIA measurements in 9 of 10 sera that were positive for TgAbs in both assays and showed compromised TgR.
16) recently showed that interference in Tg measurement by TgAbs cannot be excluded when TgAbs are not detectable.
TgAbs in sera from patients with autoimmune thyroid disease (AITD) recognize a restricted number of epitopes, whereas healthy sera exhibit an unrestricted epitope-binding pattern (7).
Hashimoto thyroiditis was diagnosed based on the presence of goiter, TgAbs and/or antithyroid peroxidase antibodies (TPOAbs), thyroid lymphocytic infiltration on cytology, and where available, thyroid ultrasound findings suggestive of chronic thyroiditis.
TgAbs (reference values <98 kIU/L) and TPOAbs (reference values <19.
All five antibodies are directed against Tg epitopes not recognized by the TgAbs present in thyroid diseases as found in previous studies (11).
We assayed Tg and TgAbs in the 153 Graves patients before treatment.
For the 87 control samples considered negative for TgAbs (<60 kilounits/L), the median recovery was 102% (range, 80-124%) compared with 82% (range, 65-98%) for the 4 TgAb-positive samples.
For 81 samples considered negative for TgAbs (<60 kilounits/L), median recovery was 101% (range, 80-115%), which was identical to the recovery for control sera (Z = -1.