Methemoglobinemia - methylene blue test
The methylene blue test is a test to determine the type or to treat methemoglobinemia, a blood disorder.
The health care provider wraps a tight band or blood pressure cuff around your upper arm. The pressure causes veins below the area to fill with blood.
The arm is cleaned with a germ killer (antiseptic). A needle is placed into your vein, usually near the inside of the elbow or back of the hand. A thin tube, called a catheter, is placed into the vein. (This may be called an IV, which means intravenous). While the tube stays in place, the needle and tourniquet are removed.
A dark green powder called methylene blue goes through the tube into your vein. The provider looks at how the powder turns a substance in the blood called methemoglobin into normal hemoglobin.
How to Prepare for the Test
No special preparation is required for this test.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
There are several types of oxygen-carrying proteins in the blood. One of them is methemoglobin. Normal methemoglobin level in blood are usually 1%. If the level is higher, you can become sick because the protein is not carrying oxygen. This can make your blood look brown instead of red.
Methemoglobinemia has several causes, many of which are genetic (problem with your genes). This test is used to tell the difference between methemoglobinemia caused by the lack of a protein called cytochrome b5 reductase and other types that are passed down through families (inherited). Your doctor will use the results of this test to help determine your treatment.
Normally, methylene blue quickly lowers the level of methemoglobin in the blood.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
You may have a rare form of methemoglobinemia if this test does not significantly lower the blood level of methemoglobin.
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Inserting an IV may be more difficult for you or your child than for other people.
Other risks associated with this type of blood test are minor, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Multiple punctures to locate veins
- Hematoma (blood accumulating under the skin causing bruising)
- Infection (a slight risk any time the skin is broken, but the chances of infection increase the longer the IV remains in the vein)
Benz EJ, Ebert BL. Hemoglobin variants associated with hemolytic anemia, altered oxygen affinity, and methemoglobinemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 43.
Chernecky CC, Berger BJ. Methemoglobin - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:781-782.