Sickle cell anemia is hallmarked by hemolysis, which releases hemoglobin (Hb) into the plasma promoting vaso-occlusive crisis (VOC). Haptoglobin (Hp) clears free Hb and decreases Hb-related pathophysiology in sickle cell anemia. There are two alleles (HP1 and HP2) and three genotypes (HP1-1, HP1-2 and HP2-2) of Hp with different frequencies in different populations. This study involved Hp level and genotype among normal and sickle cell anemia patients with varying severity of VOC. A total of 297 sickle cell anemia patients and 98 healthy controls were selected for the study. The sickle cell anemia patients were categorized as 'mild-phenotype' with no pain episodes and 'severe-phenotype' as having three or more acute pain episodes in the preceding 12 months. The Hp level was significantly lower (p < 0.001) in sickle cell patients anemia than controls; HP1-1 genotype had a higher Hp level compared to HP1-2 and HP2-2 (p < 0.05). Turkey-Kramer multiple comparison tests showed that mild and severe phenotypes have significant differences (p < 0.05) in Hb F%, Hb, platelet count, aspartate aminotransferase (AST), alanine aminotransferase (ALT), direct-bilirubin (Bil-D), total-bilirubin (Bil-T), lactate dehydrogenase (LDH) and Hp level. Pearson correlation revealed that Hp level has a positive (p < 0.05) correlation with Hb F%, Hb, packed cell volume (PCV) and serum urea; in contrast its level is negatively correlated with AST, ALT, Bil-T and LDH. A significantly higher frequency of HP2 allele and HP2-2 genotypes was found in severe phenotypes. In the studied population, it was found that higher HP2 frequency, low Hp level and more hemolysis favors the onset of VOC in sickle cell anemia.
Keywords: Haptoglobin (Hp); sickle cell anemia; vaso-occlusive crisis (VOC).