Relationship between thyroglobulin and tumor detectability with thallium-201 in differentiated thyroid cancer

Aim: Tumor scintigraphy with 201-TlCl is on established diagnostic method i n the follow-up of differentiated thyroid cancer. We investigated the relat ionship between thyroglobolin (Tg) level and tumor detectability. Subject a nd methods: We analyzed the scans of 122 patients (66 patients with proven tumor). The patient population was divided into groups with Tg above (N = 3 3) and below (N = 33) 5 ng/ml under TSH suppression or above (N = 33) and b elow (N = 33) 50 ng/ml under TSH stimulation. Tumor detectability was compa red by ROC-analysis (True-Positive-Fraction test, specificity 90%). Results : There was no significant difference (sensitivity 75% versus 64%; p = 0.55 ) for patients above and below 5 ng/ml under TSH suppression and a just sig nificant difference (sensitivity 80% venus 58%; p = 0.04) for patients abov e and below 50 ng/ml under TSH stimulation. In 18 patients from our sample with tumor, Tg under TSH suppression was negative, but 201-TlCl-scan was ab le to detect tumor in 12 patients. Conclusion: Our results demonstrate only a moderate dependence of tumor detectability on Tg level, probably without significant clinical relevance. Even in patients with slight Tg elevation 201-TlCl scintigraphy is justified.