The methylene blue test is a test to determine the type of methemoglobinemia (a blood disorder).
How the test is performed
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 health care 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, you may feel some pain or a stinging feeling. Afterward, there may be some throbbing.
Why the test is performed
There are several types of oxygen-carrying proteins in the blood. One of them is methemoglobin. Normal methemoglobin levels in blood are usually around 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. 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 rapidly lowers the levels of methemoglobin in the blood.
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
You may have a rare form of methomoglobinemia if this test does not significantly lower blood levels of methemoglobin.
What the risks are
Veins and arteries vary in size from one patient 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:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken, but the chances of infection increase the longer the IV remains in the vein)
Chad Haldeman-Englert, MD, FACMG, Wake Forest School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon.