ROC analysis in radioimmunoassay: an application to the interpretation of thyroglobulin measurement in the follow-up of thyroid carcinoma.

This study is an application of the ROC technique to the determination of threshold values (TV) for the interpretation of serum thyroglobulin (Tg) measurements in the follow-up of differentiated thyroid cancer. Serum Tg was assayed using the Henning kit in 1466 samples from 245 individuals. A local or distant recurrence was assessed by clinical examination, radiological and scintigraphic investigations, and was present in 23 patients. The measurements were divided into four groups: 1) measurements performed less than 6 months after thyroidectomy; 2) measurements performed more than 6 months after thyroidectomy; 3) measurements performed during the suppression of pituitary secretion; 4) measurements performed during withdrawal of the substitutive therapy. An ROC curve was calculated for each group and for each curve three TVs were determined: TV1, TV2, and TV3 corresponding to a high sensitivity, a high specificity and a high sum of sensitivity and specificity respectively. TV1 is 3.12 micrograms/l in the four groups. TV2 is 44 micrograms/l, 19 micrograms/l, 11 micrograms/l and 30 micrograms/l, in the first, second, third and fourth groups respectively. TV3 is 35 micrograms/l in the first group, 3.12 micrograms/l in both the second and third groups and 30 micrograms/l in the fourth group. When the classical method allows the determination of only one threshold value, the ROC technique allows us to determine threshold values adapted to both the patient clinical status and the chosen sensitivity or specificity.