Methylene blue test

How the test is performed:

An angiocatheter (IV) is usually placed in a vein (venipuncture), typically from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and then removed while the angiocatheter is left in the vein. The tourniquet is then removed to restore circulation.

A quantity of methylene blue, based on weight (1-2 mg/kg), is then injected into the vein.

Note: mg/kg = milligrams per kilogram

How to prepare for the test:

If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. This test requires temporary placement of an angiocatheter, an IV, and this should be explained to your child. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

How the test will feel:

When the needle is inserted, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

Methemoglobinemia has several causes, many of which are genetic. This tests assists in distinguishing between methemoglobinemia caused by a deficiency of NADH cytochrome b5 reductase, and certain types of hereditary methemoglobinemia caused by hemoglobin M disease.

Most methemoglobinemia quickly responds to IV administration of methylene blue, and can be controlled by daily doses of oral methylene blue and ascorbic acid. However, some types of hereditary methemoglobinemia do not respond to methylene blue. This test allows distinction between the two, and helps your health care provider develop a plan of care.