Comparison between serum calcitonin (CT) levels following Pentagastrin (Pg) and Calcium (CA) stimulus
Valeria Bottici, Mariangela Sculli, Giulia Renzini, Paolo Passannanti, Fabiana Lucchetti, Lucia Grasso, Aldo Pinchera & Rossella Elisei
Serum CT is the most specific marker of Medullary Thyroid carcinoma (MTC). Although Pg test is the most frequently used to induce CT secretion, the poor availability of Pg makes it necessary to look for different agents. Aim of this work was to compare the induction of CT secretion following 2 different stimuli in the same patient. We studied 25 patients (14 females, 11 males; mean age 50±15 yrs; range 1277 yrs). All patients were subjected to both tests by injection of 0.5 μg/kg of Pg and 2 mg/kg of CA in 5 fminutes. Thirteen/25 patients showed undetectable basal CT (<10 pg/ml); these cases were already treated with total thyroidectomy. Six/13 patients showed undetectable CT levels both after Pg and CA stimulation and were disease-free. In 2 patients CT was elevated both after Pg (mean 37 pg/ml, range 1163) and CA (mean 22 pg/ml, range 2123). Imaging was negative (biochemical persistence of disease, BP). In 5/13 patients CT was undectable after CA but not after Pg (mean 33 pg/ml, range 11114); all of them were BP. In12 patients basal CT was detectable (mean 980±1782 pg/ml, range 62-4590 pg/ml). In all patients CT peak after Pg and CA was higher than basal CT (mean 3196 pg/ml, range 65-17990; mean 1522 pg/ml, range 60-9650, respectively). Six/12 patients had a metastatic disease, 3/12 showed a BP, 3/12 were under presurgical investigation for MTC. In summary, we demonstrated that Pg and CA test give similar results in 20/25 cases, although CT levels after CA injection are lower than after Pg. In 5 cases the CA test was negative while Pg test was positive with moderate levels of CT. These patients were already been subjected to thyroidectomy for MTC and they would be considered erroneously as disease free on the basis of CA test. In conclusion, Pg test is more sensitive than CA test in patients with basal undectable CT levels. It has a similar sensitivity in patient with elevated basal CT. Although CA stimulation induces a lower secretion of CT than Pg, we propose that CA test is useful in the diagnosis and follow-up of these patients. Patients, already treated by surgery, showing a negative CA test should repeat this test before declaring them as disease-free.