Haptoglobin 1 Allele Predicts Higher Serum Haptoglobin and Lower Multiorgan Failure Risk in Sickle Cell Disease.

Haptoglobin (HP) is an acute phase protein and the main scavenger of cell-free hemoglobin. When haptoglobin is depleted, as observed in hemolytic conditions such as sickle cell disease (SCD), cell-free hemoglobin can lead to acute organ damage. The impact of the HP 1-1, 2-1, and 2-2 isoforms on HP and cell-free hemoglobin concentrations and SCD-related complications is unclear. In a longitudinal cohort of SCD patients, the HP 1 allele was associated with higher HP and lower cell-free hemoglobin concentrations at a routine clinic visit as well as during hospitalization for a vaso-occlusive episode (VOE) or acute chest syndrome. With a median follow up of 6.8 years, acute chest syndrome occurred in 42% (n=163) and multiorgan failure in 14% (n=53) of 391 SCD patients with a minimum follow-up of six months. The HP 1 allele was independently associated with lower risk of developing multiorgan failure during acute chest syndrome (additive model HR 0.5; P<0.001). Future studies assessing the regulation of HP concentrations and ability to bind cell-free hemoglobin according to HP genotype may help to identify SCD patients at high risk for multiorgan failure and to guide interventions, such as rapid initiation of exchange transfusion or HP replacement therapy.