The P50 of sickle cell hemoglobin is

The P50 of sickle cell hemoglobin is

• A. 19 mm Hg
• B. 26 mm Hg
• C. 31 mm Hg
• D. 35 mm Hg

Answer: (C)

P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated. In sickle cell hemoglobin (HbS), the oxygen affinity is reduced compared with normal Hb, so the dissociation curve shifts to the right. That means a higher PO2 is needed to achieve 50% saturation, i.e., a higher P50. Normal HbA has a P50 of about 26–27 mm Hg; HbS sits higher, typically around 30–32 mm Hg. Among the options, 31 mm Hg best matches the expected P50 for HbS. This higher P50 means that at the same arterial PO2, HbS is more in the deoxygenated state, which favors polymerization and sickling under hypoxic or acidic conditions.

P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated. In sickle cell hemoglobin (HbS), the oxygen affinity is reduced compared with normal Hb, so the dissociation curve shifts to the right. That means a higher PO2 is needed to achieve 50% saturation, i.e., a higher P50. Normal HbA has a P50 of about 26–27 mm Hg; HbS sits higher, typically around 30–32 mm Hg. Among the options, 31 mm Hg best matches the expected P50 for HbS. This higher P50 means that at the same arterial PO2, HbS is more in the deoxygenated state, which favors polymerization and sickling under hypoxic or acidic conditions.