Background: Vitamin A deficiency reduces retinol binding protein (RBP) but not transthyretin (TTR), while inflammation reduces both RBP and TTR and increases C-reactive protein (CRP), an acute phase reactant. Objective: To estimate serum RBP, TTR, and CRP in ELBW infants to test the hypotheses that (a) TTR is a negative acute phase reactant and (b) a higher RBP/TTR ratio or CRP is associated with death/BPD by 36 weeks corrected age. Design/Methods: Serum RBP, TTR, and CRP were measured in 79 ELBW infants at 28 days. Area under the curve (AUC) of receiver operating characteristic curve analysis evaluated the predictive value of TTR, the RBP/TTR ratio, and CRP for death/BPD at 36 weeks. Results: (1) TTR inversely correlated with CRP (r = -0.45, p<0.0001) consistent with TTR being a negative acute phase reactant. (2) The RBP/ TTR ratio predicted death/BPD (AUC 0.68 (CI 0.57 to 0.78)). (3) CRP strongly predicted death/BPD (AUC 0.85 (CI 0.76 to 0.92)), even after exclusion of sepsis. Conclusions: A higher CRP and RBP/TTR molar ratio on day 28 are associated with death/BPD at 36 weeks in ELBW infants. Lower TTR and maintained RBP/TTR ratios suggest inflammation rather than vitamin A deficiency as the cause for lower serum vitamin A levels in ELBW infants. © 2005 Nature Publishing Group All rights reserved.