IngentaConnect Does a highly sensitive thyroglobulin (Tg) assay change the clini...

Abstract:

Summary Objective

To evaluate a highly sensitive thyroglobulin (Tg) assay [functional sensitivity (FS): 0·1 ng/ml] (Tg-ICMA) in low-risk patients with known Tg on T4 ≤ 1 ng/ml measured by a traditional assay (FS: 1 ng/ml) (Tg-IRMA). Methods

Tg-ICMA was measured in serum samples stored at -70 °C. Samples were obtained 6 months or more after total thyroidectomy and remnant ablation with ¹³¹I, during L-T4 therapy (TSH < 0·4 mIU/l). All patients had well-differentiated and completely resected tumours, no ectopic uptake on post-therapy whole-body scans and were considered to be at low risk for recurrence. On the occasion of collection and retesting for this study, Tg-IRMA was ≤ 1 ng/ml in all samples and no antibody interference was observed. Results

Tg-ICMA ≤ 0·1 ng/ml was observed in 130/178 (73%) patients and recurrence was diagnosed in only 1/130 (0·8%). Tg-IRMA measured after L-T4 withdrawal was > 1 ng/ml in 5/130 (3·8%) patients. Forty-eight (27%) patients had Tg-ICMA > 0·1 ng/ml (0·12-1·6 ng/ml) and recurrence was diagnosed in 5/48 (10·5%). Tg-IRMA measured after L-T4 withdrawal was > 1 ng/ml in 20/48 (41·6%) patients. A negative predictive value of 100% was achieved with Tg-ICMA on T4 ≤ 0·1 ng/ml combined with neck ultrasonography (US) or with stimulated Tg-IRMA ≤ 1 ng/ml. Conclusions

Patients at low risk for recurrence with undetectable Tg on T4 measured by a highly sensitive assay (FS: 0·1 ng/ml) in the absence of antibody interference and with a negative sensitive neck US do not need to be submitted to Tg stimulation. Recurrence is rare in these cases and only a minority of patients convert to stimulated Tg > 1-2 ng/ml.

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Does a highly sensitive thyroglobulin (Tg) assay change the clinical management of low-risk patients with thyroid cancer with Tg on T4 < 1 ng/ml determined by traditional assays?