Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

METR
9322
MEVP
84159
other causes, such as congenital heart disease
Interpretation: In congenital methemoglobinemia, the methemoglobinemia concentration in blood is
about 15% to 20% of total hemoglobin. Such patients are mildly cyanotic and asymptomatic. In acquired
(toxic) methemoglobinemia, the concentration may be much higher. Symptoms may be severe when
methemoglobin is >40% of hemoglobin. Very high concentrations (>70%) may be fatal.
Reference Values:
METHEMOGLOBIN
0-11 months: not established
> or =1 year: 0.0-1.5% of total hemoglobin
SULFHEMOGLOBIN
0-11 months: not established
> or =1 year: 0.0-0.4% of total hemoglobin
Clinical References: Beutler E: Methemoglobinemia and other causes of cyanosis. In Hematology.
6th edition. Edited by WJ Williams, E Beutler, AJ Erslev, MA Lichtman. New York, McGraw-Hill Book
Company, 2001, pp 611-614
Methemoglobin Reductase, Blood
Clinical Information: Methemoglobin reductase, also called "diaphorase," and more properly called
cytochrome B(5) reductase, is the only enzyme within the erythrocyte that maintains hemoglobin in the
reduced (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 reductase deficiency have
normal arterial oxygen saturation but have varying quantities of methemoglobin in their blood, generally
15% to 20%, and are quite cyanotic. Paradoxically, homozygotes have normal blood counts; the condition
does not cause polycythemia. The reason for this apparent paradox seems to be that the presence of
methemoglobin shifts the hemoglobin-O(2) dissociation curve to the right, so that although the transport
of oxygen is diminished, the delivery of oxygen to tissues is normal. The condition is quite benign, but
may cause concern to parents of affected children, be a cosmetic embarrassment to the children, and alarm
the attending physician. The cyanosis may be treated with methylene blue.
Useful For: Confirming cases of heterozygous or homozygous methemoglobin reductase deficiency
Genetic studies in families with methemoglobin reductase deficiency
Interpretation: Methemoglobin reductase activity in neonates (0-6 weeks) 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 methemoglobin reductase activity
and increased levels of methemoglobin.
Reference Values:
8.2-19.2 IU/g hemoglobin
Clinical References: Beutler E: Methemoglobinemia and other causes of cyanosis. In Williams
Hematology. 6th edition. Edited by E Beutler, M Lichtman, WJ Williams, TJ Kipps. New York,
McGraw-Hill Book Company, 2001, p 611
Methemoglobinemia Evaluation
Clinical Information: Methemoglobin: Methemoglobinemia, with or without sulfhemoglobinemia, is
most commonly encountered as a result of administration of such medications as phenacetin,
phenazopyridine, sulfonamides, local anesthetics, dapsone, or following ingestion of nitrites or nitrates.
Congenital methemoglobinemias are rare. They are due either to: -A deficiency of methemoglobin
reductase (also called cytochrome B5 reductase or diaphorase) in erythrocytes, an autosomal recessive
disorder -One of several intrinsic structural disorders of hemoglobin, called methemoglobin-M, all of
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