A Comparison of Pentagastrin Injection and Calcium Infusion as Provocative Agents for the Detection of Medullary Carcinoma of the Thyroid1

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Abstract
The relative effectiveness of pentagastrin injection and calcium infusion as clinical stimulatory tests for the detection of medullary thyroid carcinoma (MCT) were compared. A specific radioimmunoassay for human thyrocalcitonin (TCT) was used to measure secretory responses. Tests were conducted with 38 patients having either surgically proven MCT or a positive family history of the disease. Base line plasma TCT levels were clearly elevated (1.4 to 455 ng/ml) in 7 patients and were undetectable (less than 0.24 ng/ml) in 31. Each patient was tested by giving, on separate days, a rapid intravenous injection of pentagastrin (0.5 μg/kg) and an intravenous infusion of calcium gluconate (15 mg Ca/kg/4 hr). All 7 patients with elevated base line levels of plasma TCT showed positive responses to both pentagastrin and calcium. In three patients the mean peak response to calcium occurred 30 min after the beginning of the infusion with mean plasma TCT rising approximately 5-fold above base line. The peak response to pentagastrin occurred 2 min after the injection and averaged 10- to 11-fold above base line. While TCT levels remained elevated throughout the calcium infusion, the responses to pentagastrin injection were of shorter duration, returning to base line by 30 to 60 min. Three patients in the group of 31 without elevated base line levels of TCT, showed clear cut elevations in TCT after pentagastrin injection but not during calcium infusion. All 3 subsequently were shown by surgery to have small foci of medullary carcinoma. The results suggest that pentagastrin injection can elicit a more rapid and intense TCT secretory response than a standard calcium infusion test in patients with MCT. Our experience to date further suggests that a pentagastrin injection may constitute a rapid and convenient provocative test for increased secretion of TCT and be especially valuable for the diagnosis of MCT in its early subclinical stages.