Do thyroid cancer patients with basal undetectable Tg measured by current immunoassays require rhTSH testing?
OBJECTIVE
To evaluate the predictive value of disease free status of basal thyroglobulin (Tg) in differentiated thyroid carcinoma (DTC).


METHODS
Basal and recombinant human TSH (rhTSH) stimulated Tg measured with a commercial immunoassay (Liaison DiaSorin, Italial), neck ultrasonography (US) and fine needle aspiration cytology if required were performed in DTC patients followed prospectively for 6.8 years in a university hospital. 92 consecutive DTC patients were included. 74 patients with basal and stimulated Tg <1.0 ng/ml and Tg antibodies and US negative were considered as disease-free and persistent/recurrent disease was detected in 18 patients. In 25/74 disease-free patients rhTSH test was repeated within one year.


RESULTS
63/92 patients had undetectable basal Tg (<0.5 ng/ml), with rhTSH-Tg <0.5 ng/ml in 52, in 6 rhTSH-Tg between 0.5 and 1 ng/ml, in 2 between 1-2 ng/ml (disease-free after 3 years of follow-up) and >2.0 ng/ml (mean 4.1±2.4 ng/ml) in another 3, with US lymphatic metastasis confirmed histologically. Disease-free state was predicted with a sensitivity (S) of 66.7% and specificity (Sp) of 75.7% for basal Tg-0.5 ng/ml, and S 100% and Sp 85.1% for stimulated Tg-0.92. rhTSH test and US were repeated within one year in 25 disease-free patients with Tg<1.0 ng/ml. No further elevation below 1 ng/ml was observed.


CONCLUSIONS
Low risk patients with undetectable basal Tg measured with current commercially available immunoassays should be followed with at least one rhTSH stimulated Tg and neck US because of the insufficient predictive value for recurrence/persistent disease of basal Tg.
Servei de Endocrinologia i Nutrició, Hospital Clínic, Barcelona, Spain. diazsotogonzalo@gmail.com
G
G
Díaz-Soto
M
M
Puig-Domingo
I
I
Martínez-Pino
M J
MJ
Martínez de Osaba
M
M
Mora
F
F
Rivera-Fillat
I
I
Halperin
D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000097:blood / Q000175:diagnosis*; D003940:Diagnostic Techniques, Endocrine / Q000592:standards / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000592:standards; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011994:Recombinant Proteins / Q000032:analysis; D012016:Reference Values; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000032:analysis / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis*; D013972:Thyrotropin / Q000032:analysis / Q000097:blood
D011994:Recombinant Proteins; D013972:Thyrotropin; D013954:Thyroglobulin