Serum tryptophan and serum serotonin during bone marrow transplant. Note the logarithmic scales. (A) Tryptophan levels in the serum of pediatric patients undergoing bone marrow transplant (BMT) increased from baseline to day 14 posttransplant (11.87 μg/mL [10.36-16.35] vs 14.74 μg/mL [10.69-20.40]; P = .012) when the cohort is pooled. Trendlines show the change during transplant for each individual patient. (B) Patients without FA exhibit increased serum tryptophan levels from baseline to day 14 posttransplant (10.98 μg/mL [8.71-15.01] vs 15.66 μg/mL [11.81-25.44]; P = .029), whereas patients with FA were stable (12.28 μg/mL [10.16-16.75] vs 17.73 μg/mL [12.37-25.35]; P = .061), with no difference between the 2 groups at either time point (baseline, 10.98 μg/mL vs 12.28 μg/mL [9.92-17.00], P = .37; day 14, 15.66 μg/mL vs 17.73 μg/mL [12.30-25.20], P = .27). (C) Serum serotonin increased significantly after HSCT when patients with and without FA are pooled (128.09 ng/mL [41.00-259.65] vs 212.27 ng/mL [64.10-1949.59]; P = .029). (D) Patients without FA exhibit a decrease in serum serotonin during transplant (187.95 ng/mL [58.75-342.95] vs 75.66 ng/mL [28.36-151.37]; P = .019), whereas patients with FA display a marked increase in serum serotonin during transplant (89.24 ng/mL [40.24-192.03] vs 2063.96 ng/mL [1143.87-3181.55]; P < .0001). Trendlines show the change during transplant for individual patients in each group. (E) Serum serotonin values were further evaluated at day 42, showing a gradual decrease in serotonin for patients with FA (1320 ng/mL [484.78-2653.79]; P = .024) compared with day 14, whereas patients with other diagnoses were unchanged (67.01 ng/mL [23.07-166.77]; P = .74). (F) Serum serotonin levels at day 14 in patients with other diagnoses (without FA) were similar to those without FA who also received CD34⁺-selected grafts, whereas patients with FA who all received CD34⁺-selected grafts were significantly higher at day 14 compared with non-FA CD34⁺-selected graft recipients (2063.96 ng/mL [1143.87-3181.55] vs 43.14 ng/mL [25.91-156.50]; P < .0001). (G) Serum serotonin is lower at baseline in patients with bone marrow failure (not FA) than in those with FA (8.58 ng/mL [2.93-23.25] vs 89.24 ng/mL [40.24-192.03]; P < .0001) and remains essentially unchanged in patients with bone marrow failure (not FA) after HSCT (8.58 ng/mL [2.93-23.25] vs 9.12 ng/mL [1.98-13.30]; P = .69).