Background Extracellular haemoglobin (Hb) is toxic and causal in pro-inflammation, oxidative stress and subsequent induction of down-stream mechanisms leading to cell death. Very preterm infants have low circulating levels of haptoglobin, the main endogenous scavenger of extra-cellular haemoglobin. Extracellular haemoglobin and its oxidised metabolite, methemoglobin (metHb), may be a principal inducer of pro-inflammation and oxidative stress leading to organ damage in very preterm infants.

Aim Evaluate the relationship between circulating levels of extracellular haemoglobin metabolites, endogenous haemoglobin-scavengers and markers of pro-inflammation.

Material/methods Prospective study of 64 very preterm infants with a mean (SD) gestational age of 26.4 (1.9) weeks and birth weight of 888 (288) g. Concentrations of extracellular Hb and its metabolites (oxyhemoglobin, methemoglobin), haptoglobin, hemopexin, soluble CD163, TNFa, IL-1b, IL-6, IL-10, monocyte chemoattractant protein-1 (MCP-1) and MMP-9 were measured at 24 h of age through an indwelling arterial catheter. Iatrogenic hemolysis was carefully avoided during sampling and subsequent handling.

Results Median (range) concentrations of extracellular Hb were 145.4 (0.1–1718) microg/L, oxyHb 14.3 (5.6–156.3) mM, metHb 1.4 (0.1–31.5) mM, haptoglobin 34.4 (0.1–955) microg/L, hemopexin 0.25 (0.01–0.79) microg/L and CD163 0.7 (0.1–1.9) microg/L. There was an inverse correlation between levels of extracellular Hb and haptoglobin, (r= - 0.69 (p = 0.001)) and hemopexin (r=-0.64 (p = 0.001)). Incresed levels of metHb correlated with those of MCP-1 (r = 0.35, p = 0.01) and of TNFa (r = 0.30, p = 0.02).

Conclusion Very preterm infants had high levels of extracellular Hb metabolites clearly overwhelming the endogenous haptoglobin scavenging system. Levels of the oxidised extracellular Hb metabolite, methemoglobin, correlated with markers of pro-inflammation. Supplementary treatment with a haemoglobin scavenger may be of importance in very preterm infants.