Letters Section Editor: Robert M. Golub, MD, Senior Editor.
In Reply: Dr Waugh raises the potential role of citrulline supplementation as a mechanism to increase arginine levels. A carefully designed trial to compare the efficacy of oral arginine vs citrulline may be worthwhile, particularly in children. However, citrulline levels are generally higher in adult patients with pulmonary hypertension and correlate with rising creatinine levels,1 suggesting impaired ability of kidneys to convert citrulline to arginine. Although we found that the ratio of arginine to ornithine was an excellent biomarker of arginase activity in this patient population and correlated with severity of pulmonary hypertension and mortality, including citrulline in the denominator of this ratio (arginine/[ornithine + citrulline]) identified a group of patients at even greater risk of early death. Therefore, patients with renal dysfunction and secondary accumulation of citrulline may require special consideration, as chronic end-organ damage to the kidney is common in patients with SCD and pulmonary hypertension and is associated with increased risk of death.2
Morris CR, Vichinsky EP, Kato GJ, Gladwin MT, Hazen S, Morris SM. Arginine Metabolism, Pulmonary Hypertension, and Sickle Cell Disease—Reply. JAMA. 2005;294(19):2432-2434. doi:10.1001/jama.294.19.2433-b