Isoleucine Quantitative Plasma Test

This test measures the concentration of isoleucine in your blood, an amino acid that regulates sugar in the body.

• To determine if there are any metabolic disorders or inborn metabolic errors affecting isoleucine levels
• To diagnose and monitor Maple Syrup Urine Disease (MSUD), a rare genetic condition that inhibits the body’s ability to break down certain amino acids, including isoleucine

A doctor may recommend this test if there is a suspicion of MSUD based on clinical history or provisional clinical diagnosis. This test can also be recommended for

• Infants if the parents have a family history of metabolic disorders.
• Anyone experiencing symptoms like failure to thrive (i.e. abnormal growth and development), lethargy, seizures, and developmental delays.

Elevated isoleucine levels in plasma may indicate MSUD or other metabolic disorders. Low levels may indicate malnutrition or other underlying health conditions. 

This test involves drawing a small sample of blood from a vein in your arm with a needle and a syringe. You may feel a slight pinch as the needle is inserted.

Your doctor may advise you to fast for up to 8 hours before the test. If you're taking any amino acid supplements or medications that affect isoleucine levels, your doctor may recommend stopping them before the test. Fasting before the test is recommended but not mandatory. It is advisable to consult your healthcare provider to determine if there are any particular requirements you should be aware of.

If MSUD is suspected, other tests such as leucine loading test and enzyme assays may also be conducted.

Isoleucine assay or plasma isoleucine test

Maple Syrup Urine Disease (MSUD) is a rare genetic disorder that occurs when the body cannot break down certain amino acids, such as leucine, isoleucine, and valine properly. These amino acids build up in the body and can cause severe brain damage, seizures, coma or even death if left untreated.