Monitoring the treatment of carcinoid disease using blood serotonin and plasma 5-hydroxyindoleacetic acid: three case examples.

The results for plasma 5-hydroxyindoleacetic acid (5-HIAA), whole blood serotonin and the chromogranins on three patients following their treatment for carcinoid disease with somatostatin analogues are presented. Two of the patients (a 56-year-old woman and a 55-year-old man) demonstrated a good clinical response following treatment, with initial high blood serotonin and plasma 5-HIAA concentrations showing a significant decline. However, blood serotonin concentrations remained above the reference range during the course of treatment, whereas plasma 5-HIAA remained borderline high or marginally elevated with respect to the clinical cut-off concentration. The third patient, a 79-year-old man, demonstrated saturation of platelets with serotonin and increasing elevation of plasma 5-HIAA, which later fell with the introduction of interferon into this patient's treatment regimen. Results for the plasma chromogranin fragments, pancreastatin (Chromogranin A) and GAWK (Chromogranin B), showed a much greater degree of variability in all three cases. This study shows promise for plasma 5-HIAA as a useful marker for monitoring carcinoid disease. The limitations of blood serotonin expressed to the platelet count are highlighted.