Thyroglobulin Measurement

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Thyroglobulin Measurement

• Elizabeth Holmes
• Royal Liverpool University Hospital

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Thyroglobulin
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Thyroglobulin (Tg)

• No role in the diagnosis of thyroid cancer.
• In patients with total thyroidectomy and 131I
  ablation Tggt2ng/mL
• Residual/recurrent tumour
• Normal thyroid remnant
• Sensitivity increased by TSH stimulation
• Always measure TFTs
• If patient in remission, measure Tg when TSH is
  suppressed

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Thyroglobulin Antibodies (TgAb)

• Present in 15-30 of patients with thyroid cancer
• Reasons for measurement
• Check for Ab interference in Tg assay
• Serial measurements may be useful as a prognostic
  indicator
• Measured by sensitive immunoassay

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Aims of the Study

• To compare 3 Tg assays
• Manual RIA
• Roche E170
• DPC Immulite 2000
• To assess 2 TgAb assays
• Roche E170
• DPC Immulite 2000

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Tg lt 5ng/mL by RIA (n51)
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Tg lt 5ng/mL by RIA (n51)
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Tg lt 5ng/mL by RIA (n51)
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Tg gt 5ng/mL by RIA (n26)
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Tg gt 5ng/mL by RIA and ICMA
E170
Immulite 2000
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Tg gt 5ng/mL by RIA (n36)
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Tg gt 5ng/mL by RIA (n36)
22/23 of these samples TgAb POSITIVE
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Spiking Experiments

• 300µL sample 75µL spike (841ng/mL)
• Acceptable recovery 70-130

• TgAb not interfering in immunometric assays
• Spiking experiments insensitive TgAb detection

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Control Experiments

• Patients who have not had a thyroidectomy
• TgAb and TPOAb ve
• Expected to have Tg gt 2ng/mL

TgAb can cause ve interference in ICMA assays
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TgAb Detection
Any detectable TgAb may cause interference in Tg
assay
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TgAb Detection Rates

• lt2 by RIA Tg dilution
• High LOQ
• TgAb present may not interfere
• 13 E170
• 11 Immulite 2000

Lower than previously published data!

• Accurate reflection of sample population
• TgAb underdetection

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Conclusions

• TgAb ve
• Good agreement between all 3 methods
• Immunometric assays have lower LOQ
• Failure to detect TgAb may not exclude Ab
  interference
• TgAb ve
• Highly discrepant Tg results
• Careful clinical monitoring required

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Acknowledgements

• Dr LM Bailey
• Prof WD Fraser
• Brian Saunders and Roche

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Any Questions?