Supplementary Material for: Haptoglobin Administration for Intravascular Hemolysis: A Systematic Review

Introduction
Exogenous haptoglobin administration may enhance plasma-free hemoglobin (pfHb) clearance during hemolysis, and reduce its end-organ damage: we sought to systematically review and summarize available evidence on the use of haptoglobin as a treatment for hemolysis of any cause.

Methods
We included studies describing haptoglobin administration as treatment or prevention of hemolysis-related complications. Only studies with a control group reporting at least one of the outcomes of interest were included in the quantitative synthesis. Primary outcome was the change in pfHb concentration 1 hour after haptoglobin infusion.

Results
Among 573 articles, 13 studies were included in the review (677 patients, 52.8% received haptoglobin). Median initial haptoglobin intravenous bolus was 4000 (2000, 4000) IU. Haptoglobin was associated with lower pfHb 1 hour (SMD -11.28; 95% CI -15.80 to -6.75; p<0.001) and 24 hours (SMD -2.65; 95% CI -4.73 to -0.57; p=0.001) after infusion. There was no difference in all-cause mortality between haptoglobin-treated patients and control group (OR 1.41; 95% CI 0.49 to 4.95; p=0.520). Haptoglobin was associated with a lower incidence of acute kidney injury (OR 0.64; 95% CI 0.44-0.93; p=0.020). No adverse events or side effects associated with haptoglobin use were reported.

Conclusions
Haptoglobin administration has been used in patients with hemolysis from any cause to treat or prevent hemolysis-associated adverse events. Haptoglobin may reduce levels of pfHb and preserve kidney function without increase in adverse events.