Platform
Company
Body Fluids
Review status
Currently under review
Pending specialist review and validation.
The CSF Leucine test measures the amount of leucine, an essential branched-chain amino acid, in your cerebrospinal fluid, the clear liquid that cushions your brain and spinal cord. Leucine is important for energy use and protein building in the nervous system.
Clinicians usually order this test as part of a cerebrospinal fluid amino acid profile when investigating unexplained neurologic symptoms, suspected inherited metabolic disorders, or possible problems with amino acid transport into the brain. Because CSF reflects the brain’s environment more directly than blood, this test can complement plasma amino acid testing to provide a clearer picture.
Abnormal leucine levels in CSF can point to conditions that affect the breakdown or movement of branched-chain amino acids, including maple syrup urine disease, as well as changes from severe illness, trauma, or liver dysfunction. Your clinician may request this test when evaluating seizures, developmental concerns, altered mental status, or to monitor a known metabolic condition.
Results are most useful when interpreted alongside other amino acids and blood tests. Patterns can help distinguish a genetic enzyme deficiency from nutritional imbalance or secondary changes due to another medical issue, guiding decisions about further testing and treatment.
Interpreting a CSF leucine result depends on your age, symptoms, and the pattern of other amino acids. If leucine is higher than expected, your clinician may confirm with plasma amino acids, review dietary intake and supplements, and consider genetic testing if an inherited disorder is suspected. A mild change that does not fit your clinical picture may lead to a repeat test, especially if there was a chance of blood contamination in the CSF sample.
If leucine is lower than expected, your team may look at overall nutritional status, protein intake, and possible transport issues. Regardless of the direction of change, next steps are individualized and may include repeat sampling, dietary adjustments, targeted metabolic studies, or referral to a specialist in inherited metabolic diseases.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
High protein intake, prolonged fasting, or rapid weight loss can shift amino acid levels in blood and, to a lesser degree, in CSF, which may influence interpretation.
Even small amounts of blood introduced during a lumbar puncture can raise CSF amino acid concentrations, including leucine, leading to falsely high results.
Amino acid infusions, total parenteral nutrition, or leucine-containing supplements used for sports or recovery can elevate measured leucine.
Fever, infection, trauma, or major surgery increases protein breakdown, which can alter branched-chain amino acids and complicate result interpretation.
Liver dysfunction impairs amino acid metabolism and kidney disease alters clearance, both of which can change leucine levels in body fluids.
Delayed transport, improper storage, or lack of prompt freezing can affect amino acid stability. Correct handling supports reliable results.
References