Clinical laboratory verification of thyroglobulin concentrations in the presence of autoantibodies to thyroglobulin: comparison of EIA, radioimmunoassay and LC MS/MS measurements in an Urban Hospital

Abstract

ObjectiveThyroglobulin (Tg) measurements assess recurrence in post-thyroidectomy thyroid cancer patients. Tg measurements by enzyme immunoassays (EIA) can be falsely elevated by interference from Tg autoantibodies (TgAb). Radioimmunoassay (RIA) is less susceptible to TgAb interference and has been the standard-of-care test for TgAb positive patients. Recently developed liquid chromatography tandem mass spectrometry (LC–MS/MS) methods may eliminate TgAb interference. We assessed the performance of Tg measurements by EIA, RIA and LC–MS/MS to evaluate TgAb interference differences.ResultsWe measured TgAb and Tg in 50 plasma samples from 40 patients in whom Tg measurement was part of their routine follow-up and 10 healthy volunteers. Discrepancy between EIA and both LC–MS/MS and RIA was observed at low Tg concentrations (≤ 7.55 ng/mL) in TgAb positive specimens (LC–MS/MS = 1.9 * EIA − 0.03, r = 0.68). RIA and LC–MS/MS Tg measurements in TgAb positive specimens with low Tg concentrations had improved correlation but demonstrated bias (LC MS/MS = 0.6 * RIA − 1.4, r = 0.90). Disagreement between methods may be attributed to LC–MS/MS reported Tg concentrations as undetectable compared to RIA. It seems likely that most discrepant cases are falsely elevated in RIA due to TgAb interference, however, some cases appear below the detection limit of LC–MS/MS; implementation of LC–MS/MS by clinicians will require lower detection limits.Electronic supplementary materialThe online version of this article (10.1186/s13104-017-3050-6) contains supplementary material, which is available to authorized users.

Clinical irrelevance of lower titer thyroglobulin autoantibodies in patients with differentiated thyroid carcinoma

“…In patients with lower titer TgAbs during 131 I ablation therapy, we found a clinical concordance between the Tg-IRMA and Tg-LC-MS/MS of at least 87.9%. The greater analytical disparity in the lower Tg range in patients with lower titer TgAbs (group 2) probably illustrates TgAb interference, as also noted in other studies (12,18). However, the disease outcome of these patients was reassuring, and the Tg-IRMA was still accurate in representing the clinical status during follow-up.…”

“…In addition, Rosario et al recently recommended the treatment and follow-up of patients with borderline TgAbs (between functional sensitivity and manufacturer cut-off), with an indication of an excellent response to therapy (based on ultrasound and Tg by immunoassay), could probably be the same for patients without TgAbs, so unnecessary diagnostic procedures and 131 I treatment in these DTC patients could be prevented (16). The (analytical) concordance of the Tg-IRMA and Tg-LC-MS-MS assays, in the presence of lower titer TgAbs, has been reported previously (12,17,18). Most studies used lower cut-off values to define TgAb positivity; we, however, also demonstrate a good analytical agreement between the Tg-IRMA and Tg-LC-MS/MS when a higher cut-off value is used.…”

“…Against this background, a promising technique is liquid chromatography-tandem mass spectrometry (LC-MS/MS), which digests Tg into peptides for analytical measurement, disrupting the interfering TgAbs (8). However, Tg-LC-MS/MS assays studied to date are hampered by a lack of sensitivity compared to Tg immunoassays (1,2,9,10,11,12). Laboratory Corporation of America Holdings (Labcorp, North Carolina, USA) developed a sensitive Tg-LC-MS/MS with a limit of quantification (LoQ) of 0.02 ng/mL (13), which is lower compared to previously described LC-MS/MS assays (11) and lower compared to our currently used Tg IRMA.…”