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Cytochrome b5 reductase

Cytochrome b5 reductase (CYB5R) is an enzyme in the blood. It controls the amount of iron in your red blood cells and helps the cells carry the normal amount of oxygen.

People who do not have enough of this enzyme may develop a condition called methemoglobinemia.

Cytochrome b5 reductase also has effects on liver metabolism, steroid synthesis and maintaining the body's normal acid-base status.

Alternative Names

CYB5R

Images

References

Means RT Jr. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.

Smith-Whitley K, Kwiatkowski JL. Hemoglobinopathies. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 511.

Review Date 1/10/2026

Updated by: Frank D. Brodkey, MD, FCCM, Associate Professor, Section of Pulmonary and Critical Care Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.