Stimulation test in the follow-up of thyroid cancer: plasma rhTSH levels are dependent on body weight, not endogenously stimulated TSH values.
BACKGROUND
Stimulation testing in the first year following thyroid ablation has important prognostic value in thyroid cancer patients. Recombinant human TSH (rhTSH) is better tolerated than thyroid hormone withdrawal but provides only transient stimulation so that the TSH threshold of 30 mIU x l(-1) which defines adequate testing during thyroid hormone withdrawal is not appropriate for rhTSH stimulation. We looked at rhTSH levels after a standard two intramuscular injections of 0.9 mg rhTSH.


METHODS
Plasma rhTSH levels were measured 24 h after the second injection in 143 consecutive patients.


RESULTS
rhTSH levels showed large inter-patient variation (range: 44-240; mean+/-SD: 131+/-48). There was a strong inverse correlation between TSH levels and body weight (P<0.001). Levels lower than 80 mIU x l(-1) (corresponding to 1 SD below average) were recorded in 24 patients (16.8%). These patients had an average body weight of 79.7 kg, as compared to 67.9 kg for those patients with TSH levels higher than 80 mIU x l(-1). A withdrawal test in the first year after thyroid ablation was available in 64 patients. Only one patient (1.6%) had inadequate endogenous TSH stimulation, and there was no dependence of endogenous plasma TSH levels upon weight.


CONCLUSIONS
Contrary to endogenous stimulation, TSH levels after rhTSH injection vary with body weight. The dosage of rhTSH may need to be adapted in patients with more than 80 kg body weight.
Zanotti-Fregonara
Paolo
P
Department of Nuclear Medicine, St. Antoine Hospital, Paris, France.
Duron
Françoise
F
Keller
Isabelle
I
Khoury
Alexandre
A
Devaux
Jean-Yves
JY
Hindié
Elif
E
D015415:Biomarkers / Q000097:blood; D001835:Body Weight; D005500:Follow-Up Studies; D006801:Humans; D007273:Injections, Intramuscular; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000097:blood; D013223:Statistics as Topic; D013964:Thyroid Neoplasms / Q000097:blood* / Q000175:diagnosis* / Q000532:radiotherapy; D013972:Thyrotropin / Q000008:administration & dosage / Q000097:blood*; D016896:Treatment Outcome
D015415:Biomarkers; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; D013972:Thyrotropin