methemoglobin (Hemoglobin M)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p627-628
2025-07-12
376
Type of test Blood
Normal findings
0.06-0.24 g/dL or 9.3-37.2 μmol/L (SI units)
0.4%-1.5% of total hemoglobin
Possible critical values
> 40% of total hemoglobin
Test explanation and related physiology
Methemoglobin is formed during the production of normal adult hemoglobin. If oxygenation of the iron component in the protohemoglobin occurs without subsequent reduction of the heme iron back to its Fe+2 form as exists in normal hemoglobin, excess methemoglobin accumulates. The oxidized iron form in methemoglobin is unable to combine with oxygen to carry the oxygen to the peripheral tissues. Therefore the oxyhemoglobin dissociation curve is shifted to the left, resulting in cyanosis and hypoxia.
Methemoglobinemia can be congenital or acquired. Hemoglobin M disease is a genetic defect that results in a group of abnormal hemoglobins that are methemoglobins. Another genetic mutation can cause a deficiency in reduced nicotinamide adenine dinucleotide (NADH) methemoglobin reductase enzyme, which is required to deoxygenate methemoglobin to normal adult hemoglobin. These forms of methemoglobinemia occur in infants, are usually severe, are not amenable to treatment, and are often fatal.
Acquired methemoglobinemia is a result of ingestion of nitrates (e.g., from well water) or such drugs as phenacetin, sulfonamides, isoniazid, local anesthetics, and some antibiotics. This form of the disease commonly occurs in older individuals and results in an acute crisis that is treated effectively with ascorbic acid or methylene blue. Methylene blue, however, is contraindicated in glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Interfering factors
• Tobacco use and carbon monoxide poisoning are associated with increased methemoglobin levels.
* Drugs that may cause increased levels include some antibiotics, isoniazid, local anesthetics, and sulfonamides.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: green
• Methemoglobin is very unstable. Place the specimen in an ice slush immediately after collection.
• Be prepared to provide oxygen support and close monitoring in the event the patient becomes increasingly hypoxic.
Abnormal findings
Methemoglobinemia (hereditary or acquired)
الاكثر قراءة في التحليلات المرضية
اخر الاخبار
اخبار العتبة العباسية المقدسة
