Cytochrome b5 Reductase Enzyme Activity, Blood

Clinical Use

Use

This test is used for the evaluation of patients with cyanosis and for confirming cases of suspected cytochrome b5 reductase (methemoglobin reductase) deficiency. It is also useful for conducting functional studies in families with cytochrome b5 reductase deficiency. The deficiency of CYB5R in erythrocytes is an autosomal recessive disorder resulting from variants in the CYB5R3 or the CYB5A genes, which can lead to the presence of methemoglobin causing cyanosis. Despite normal arterial oxygen saturation, individuals homozygous for CYB5R variants can exhibit symptoms like cosmetic cyanosis but generally have normal blood counts.

Special Instructions

Not provided.

Limitations

Heterozygous individuals for CYB5R genetic variants exhibit no clinical abnormalities but may experience acute episodes of methemoglobinemia when exposed to certain agents. Homozygous individuals display normal arterial oxygen saturation but have notable methemoglobin levels which may cause cosmetic cyanosis. The test results for heterozygotes may slightly fall below reference ranges whereas homozygotes will demonstrate little to no cytochrome b5 reductase activity with elevated methemoglobin levels. Caution should be exercised with individuals deficient in glucose-6-phosphate dehydrogenase as they are not suitable candidates for methylene blue therapy which can induce hemolysis.

Test Details

New York Approved