Understanding Your Blood Test: What It Measures and How to Prepare

What is this test? This is a laboratory test that helps your healthcare provider evaluate your overall health, screen for certain conditions, or monitor a known medical problem by analyzing a small sample of your blood in a certified laboratory.

The acylcarnitine test measures the levels of different acylcarnitine compounds in the blood. Acylcarnitines are substances that help transport fatty acids into cells, where they are burned for energy. When certain metabolic enzymes are missing or not working properly, these compounds can build up to harmful levels in the blood.

How is the sample collected? A trained phlebotomist will draw a small amount of blood from a vein in your arm, usually on the inside of the elbow, using a sterile needle; the procedure typically takes only a few minutes and may cause brief, mild discomfort.

For newborns, a few drops of blood are collected from the heel or finger onto a special filter paper card. This is called a dried blood spot (DBS) sample. The sample is allowed to dry and is then sent to a laboratory for testing. The collection is quick and usually done before the baby leaves the hospital.

What does the test look for? The test measures specific components in your blood, such as cells, chemicals, proteins, or markers of infection and inflammation, to help your provider detect abnormalities, track a condition over time, or assess how well your current treatment is working.

The test looks for abnormal patterns of various acylcarnitine species, including short-chain, medium-chain, and long-chain acylcarnitines. Different patterns can indicate different metabolic disorders, such as: medium-chain acyl-CoA dehydrogenase deficiency (MCAD), propionic acidemia, methylmalonic acidemia, and carnitine transport defects.

Is fasting required? Whether you need to fast depends on the specific tests your provider ordered. Some blood tests require 8 to 12 hours without food or drink other than water, so follow the instructions you were given; if fasting is not required, you may eat and drink as usual before your appointment.

For newborn screening, the test is typically done before any prolonged fasting, often within the first 24-48 hours of life. For older children or adults undergoing diagnostic testing, fasting instructions may vary. Always follow your healthcare provider's specific instructions.