Methemoglobin Reductase, Blood

CPT CODE:

USEFUL FOR:

Confirming cases of heterozygous or homozygous methemoglobinreductase deficiency
Genetic studies in families with methemoglobin reductase deficiency

SPECIMEN REQUIRED:

Draw blood in a yellow-top (ACD [solution B]) tube(s), and send 4 mL of ACD (solution B) whole blood refrigerated. Specimen cannot be frozen. Do not transfer blood to other containers.Note:    1. Patient's age is required on request form for processing.                  2.  If not ordering electronically, please complete and submit a "Hematopathology/Molecular Oncology Request Form" (Supply T241) with the specimen.

TRANSPORT TEMPERATURE:

Refrig\Ambient NO\Frozen NO

CLINICAL INFORMATION:

Methemoglobin reductase, also called "diaphorase," and moreproperly called cytochrome B(5) reductase, is the only enzymewithin the erythrocyte that maintains hemoglobin in thereduced (non-methemoglobin) state.
Persons who are heterozygous for methemoglobin reductase deficiency have no clinical or laboratory abnormalities, are not cyanotic, and have normal methemoglobin concentrations in their blood.
Persons who are homozygous for methemoglobin reductasedeficiency have normal arterial oxygen saturation but havevarying quantities of methemoglobin in their blood, generally15-20%, and are quite cyanotic. Paradoxically, homozygoteshave normal blood counts; the condition does not causepolycythemia. The reason for this apparent paradox seems tobe that the presence of methemoglobin shifts the hemoglobin-O(2)dissociation curve to the right, so that although the transport ofoxygen is diminished, the delivery of oxygen to tissues is normal.The condition is quite benign, but may cause concern to parentsof affected children, be a cosmetic embarrassment to the children,and alarm the attending physician. The cyanosis may be treatedwith methylene blue.

CLINICAL INTERPRETATION:

Methemoglobin reductase activity in neonates (0-6 weeks)is normally 60% of the normal adult value.  Adult values areattained by 2-3 months of age.
Heterozygotes have results slightly lower than the referencerange. Homozygotes demonstrate little to no methemoglobinreductase activity and increased levels of methemoglobin.

REFERENCE VALUES:

8.2-19.2 IU/g Hb