Validation of Serum Versus Plasma Measurements of Chromogranin A Levels in Patients With Carcinoid Tumors Lack of Correlation Between Absolute Chromogranin A Levels and Symptom Frequency

Objective: Chromogranin A (CGA) levels are used to confirm the diagnosis and monitor the course of patients with neuroendocrine tumors. Chromogranin A levels are significantly reduced when patients are acutely treated with octreotide; however, limited data are available that correlates octreotide long-acting repeatable (LAR) dose or steady state octreotide blood levels to the absolute value of serum or plasma CGA. Methods: Plasma, serum, and clinical information on carcinoid syndrome symptoms were collected anonymously from 40 patients treatedwith long-termoctreotide LAR therapy for carcinoid syndrome. Results: We found a strong positive linear relationship exists between serum and plasma CGA levels (r = 0.9858, P G 0.0001). No cor-relation existed between plasma octreotide levels or LAR dose and the static, absolute plasma/serum CGA levels. Although, higher mean CGA values were seen in the group whose diarrhea was Bnot under optimal control ^ than for the group Bunder optimal control,^ these results did not reach statistical significance (P = 0.24). Contrary to our hypotheses, a statistically significant inverse relationship was found between the frequency of flushing and the CGA levels (P = 0.0372). Higher mean CGA values were observed in the Bunder optimal control ^ group with flushing symptoms. Conclusions: Either serum or plasma can be used to measure CGA levels. Absolute (static) CGA levels do not positively correlate with symptom intensity during LAR therapy. Dynamic (serial) measure-ments of CGA are necessary to monitor the effectiveness of medical or surgical therapy. Key Words: neuroendocrine tumors, carcinoid, carcinoid syndrome, chromogranin A, octreotide, plasma and seru