Diaphorase; Ferrihemoglobin Reductase; Methemoglobin Reductase; Methemoglobin Diaphorase
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Cytochrome b5 Reductase Enzyme Activity, Whole Blood
Test ID: CYB5RED WB
Test
Aliases/Synonyms
Method
Kinetic Spectrophotometry
Method Description
Cytochrome b5 reductase (methemoglobin reductase) catalyzes the 1,4-dihydronicotinamide adenine dinucleotide (NADH)-linked reduction of several substrates, including ferricyanide. The activity at 37 degrees C is measured spectrophotometrically by measuring the oxidation of NADH to NAD(+) at 340 nm on an automated chemistry analyzer.
Report Includes
Cytochrome b5 Reductase
Specimens
Blood
Clinical Utility
Evaluation of patients with cyanosis
Confirming cases of suspected cytochrome b5 reductase (methemoglobin reductase) deficiency
Functional studies in families with cytochrome b5 reductase deficiency
Test Version
11-Nov-2025
Specimen
Specimens
Blood
Collection Containers
Preferred
Yellow top (ACD)
Acceptable
Lavender top (EDTA)
Sample Volume
6.0 mL
Minimum Volume
1.0 mL
Collection & Handling
Handling Information
Send whole blood specimen in original tube. Do not aliquot.
Stability
| Refrigerated | 18 days |
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Rejection Criteria
| Hemolysis | Gross |
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Test Version
11-Nov-2025
Performance / Interpretation
Method
Kinetic Spectrophotometry
Method Description
Cytochrome b5 reductase (methemoglobin reductase) catalyzes the 1,4-dihydronicotinamide adenine dinucleotide (NADH)-linked reduction of several substrates, including ferricyanide. The activity at 37 degrees C is measured spectrophotometrically by measuring the oxidation of NADH to NAD(+) at 340 nm on an automated chemistry analyzer.
Turnaround Time
10 days
Results
| Name | Units | Reference Range | Conversion Factor | |
|---|---|---|---|---|
| Cytochrome b5 Reductase | U/g Hb |
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Reference values have not been established for patients who are younger than 12 months.
Cytochrome b5 reductase (methemoglobin reductase) activity in neonates (0-6 weeks of age) is normally 60% of the normal adult value. Adult values are attained by 2 to 3 months of age.
Heterozygotes have results slightly lower than the reference range. Homozygotes demonstrate little to no cytochrome b5 reductase activity and increased levels of methemoglobin.
Individuals who are glucose-6-phosphate dehydrogenase deficient are not candidates for methylene blue therapy. Administration of methylene blue to such persons will cause hemolysis or methemoglobin formation.
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Test Version
11-Nov-2025
Interface / Setup
HL7 Interface Codes
| Order Code | Result Codes | Units |
|---|---|---|
| CYB5RED WB | 65501Cytochrome b5 Reductase, B | U/g Hb |
Test Version
11-Nov-2025