A coordinated shift toward a macrocytic and hypochromic erythrocyte phenotype in adults with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a multisystem disorder, but its hematological features remain incompletely characterized. We investigated whether erythrocyte-related indices show coordinated alterations in adults with NF1. In this retrospective single-institute study, 225 adults with NF1 were analyzed. Z-scores for erythrocyte-related parameters were calculated relative to a reference population. One-sample tests, correlation analyses, and comparisons across tumor burden (D-class) were performed. A composite score, defined as the mean of parameter-specific Z-scores, was used to assess coordinated changes. Z-scores for red blood cell count, hemoglobin, hematocrit, and mean corpuscular volume were modest but significantly increased, whereas mean corpuscular hemoglobin concentration shifted in the opposite direction. Individual effect sizes were small; however, the composite score showed a moderate effect size (Cohen's d = 0.43), indicating a coherent directional shift. Mean corpuscular volume was inversely correlated with red blood cell count (r = -0.390, P < .001), and a higher tumor burden was associated with lower mean corpuscular hemoglobin concentration. Adult patients with NF1 exhibit subtle but coordinated erythrocyte alterations, suggesting a macrocytic and relatively hypochromic profile, with erythrocyte hemoglobin concentration tending to decrease with increasing tumor burden. These findings may represent a systemic feature of NF1 and warrant further investigation.