Test Id : POX
Fatty Acid Profile, Peroxisomal (C22-C26), Serum
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluating patients with possible peroxisomal disorders, single-enzyme defects of peroxisomal metabolism, such as X-linked adrenoleukodystrophy or peroxisomal biogenesis disorders (Zellweger syndrome spectrum) using serum specimens
Aiding in the assessment of peroxisomal function
Highlights
This test analyzes very long-chain fatty acids as well as pristanic and phytanic acid to aid in diagnosis of peroxisomal biogenesis disorders, X-linked adrenoleukodystrophy (X-ALD), and Refsum disease.
This test is also appropriate for follow-up of an abnormal newborn screen for X-ALD.
Reports include concentrations of C22:0, C24:0, C26:0 species, phytanic and pristanic acid, and calculated C24:0/C22:0, C26:0/C22:0 and phytanic acid/pristanic acid ratios.
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
For more information see:
-Newborn Screen Follow-up for X-Linked Adrenoleukodystrophy
-Epilepsy: Unexplained Refractory and/or Familial Testing Algorithm
If the patient has abnormal newborn screening results for X-linked adrenoleukodystrophy, refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1)
Method Name
A short description of the method used to perform the test
Gas Chromatography Mass Spectrometry (GC-MS)
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
Adrenoleukodystrophy (ALD)
Adrenomyeloneuropathy
C22-C26, Fatty Acid Profile, Peroxisomal
Cerebrohepatorenal Syndrome
Long-Chain Fatty Acids (LCFA)
Peroxisomal, Fatty Acid Profile
Phytanic Acid
Phytanic Acid Oxidase Deficiency
Pristanic Acid
Refsum Disease
Very Long Chain Fatty Acids (VLCFA)
X-ALD (X-Linked Adrenoleukodystrophy)
X-Linked Adrenoleukodystrophy (X-ALD)
Zellweger Syndrome
ZSD
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
For more information see:
-Newborn Screen Follow-up for X-Linked Adrenoleukodystrophy
-Epilepsy: Unexplained Refractory and/or Familial Testing Algorithm
If the patient has abnormal newborn screening results for X-linked adrenoleukodystrophy, refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1)
Specimen Type
Describes the specimen type validated for testing
Serum
Necessary Information
1. Patient's age and sex is required.
2. Biochemical Genetics Patient Information (T602) is recommended, but not required, to be filled out and sent with the specimen to aid in the interpretation of test results.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Patient Preparation: Fasting 12 hours or more. (Collect specimens from infants and small children just before next feeding)
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1.5 mL
Collection Instructions: Centrifuge and aliquot serum into plastic vial.
Special Instructions
Library of PDFs including pertinent information and forms related to the test
Forms
1. Biochemical Genetics Patient Information (T602)
2. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
0.15 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Frozen (preferred) | 92 days | |
| Refrigerated | 15 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluating patients with possible peroxisomal disorders, single-enzyme defects of peroxisomal metabolism, such as X-linked adrenoleukodystrophy or peroxisomal biogenesis disorders (Zellweger syndrome spectrum) using serum specimens
Aiding in the assessment of peroxisomal function
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
For more information see:
-Newborn Screen Follow-up for X-Linked Adrenoleukodystrophy
-Epilepsy: Unexplained Refractory and/or Familial Testing Algorithm
If the patient has abnormal newborn screening results for X-linked adrenoleukodystrophy, refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1)
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Peroxisomes are organelles present in all human cells except mature erythrocytes. They carry out essential metabolic functions, including beta-oxidation of very long-chain fatty acids (VLCFA), alpha-oxidation of phytanic acid, and biosynthesis of plasmalogen and bile acids. Peroxisomal disorders include disorders of peroxisomal biogenesis with defective assembly of the entire organelle, and single peroxisomal enzyme/transporter defects where the organelle is intact but a specific function is disrupted. Peroxisomal beta-oxidation of VLCFA is impaired in all disorders of peroxisomal biogenesis and in selected single enzyme deficiencies, particularly X-linked adrenoleukodystrophy (X-ALD), resulting in elevated concentrations of VLCFA in plasma or serum.
Peroxisomal biogenesis disorders (PBD) include Zellweger syndrome spectrum disorders, which are clinically diverse and range in severity from neonatal lethal (Zellweger syndrome) to more variable clinical courses in neonatal adrenoleukodystrophy and infantile Refsum disease. Affected children typically have hypotonia, poor feeding, distinctive facial features, seizures, and liver dysfunction. Other features can include retinal dystrophy, hearing loss, developmental delays, and bleeding episodes. Rhizomelic chondrodysplasia punctata is another PBD. It is characterized by rhizomelic shortening, chondrodysplasia punctata, cataracts, intellectual disability, and seizures, although it can have a milder phenotype with only cataracts and chondrodysplasia. The typical biochemical profile shows normal VLCFA and elevated phytanic acid.
X-ALD is a neurologic disorder affecting the white matter and adrenal cortex. It can present between ages 4 and 8 years as a childhood cerebral form with behavioral and cognitive changes, associated with neurologic decline. Other forms include an "Addison disease only" phenotype with adrenocortical insufficiency without initial neurologic abnormality and adrenomyeloneuropathy associated with later-onset progressive paraparesis. X-ALD is an X-linked condition that primarily affects male patients; however, some female patients who are carriers can develop later-onset neurologic manifestations. In 2016, X-ALD was added to the US Recommended Uniform Screening Panel, a list of conditions that are nationally recommended for newborn screening by the Secretary's Advisory Committee on Heritable Disorders in Newborns and Children.
Refsum disease is a peroxisomal disorder characterized by anosmia, retinitis pigmentosa, neuropathy, deafness, ataxia, ichthyosis, and cardiac abnormalities. The classic biochemical profile of Refsum disease is an elevated plasma or serum phytanic acid level.
Biochemical abnormalities in peroxisomal disorders include accumulations of VLCFA, phytanic acid, and pristanic acid. The differential diagnosis of these disorders is based on recognition of clinical phenotypes combined with a series of biochemical tests to assess peroxisomal function and structure. These include measurements and ratios of VLCFA, pipecolic acid (PIPA / Pipecolic Acid, Serum; PIPU / Pipecolic Acid, Random, Urine), phytanic acid and its metabolite pristanic acid. In addition, confirmatory testing for X-ALD (XALDZ / X-Linked Adrenoleukodystrophy, Full Gene Analysis, Varies) via molecular genetic analysis is available.
Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
C22:0
< or =96.3 nmol/mL
C24:0
< or =91.4 nmol/mL
C26:0
< or =1.30 nmol/mL
C24:0/C22:0 RATIO
< or =1.39
C26:0/C22:0 RATIO
< or =0.023
PRISTANIC ACID
0-4 months: < or =0.60 nmol/mL
5-8 months: < or =0.84 nmol/mL
9-12 months: < or =0.77 nmol/mL
13-23 months: < or =1.47 nmol/mL
> or =24 months: < or =2.98 nmol/mL
PHYTANIC ACID
0-4 months: < or =5.28 nmol/mL
5-8 months: < or =5.70 nmol/mL
9-12 months: < or =4.40 nmol/mL
13-23 months: < or =8.62 nmol/mL
> or =24 months: < or =9.88 nmol/mL
PRISTANIC/PHYTANIC ACID RATIO
0-4 months: < or =0.35
5-8 months: < or =0.28
9-12 months: < or =0.23
13-23 months: < or =0.24
> or =24 months: < or =0.39
Interpretation
Provides information to assist in interpretation of the test results
Reports include concentrations of C22:0, C24:0, C26:0 species, phytanic acid and pristanic acid, and calculated C24:0/C22:0, C26:0/C22:0 and phytanic acid:pristanic acid ratios. When no significant abnormalities are detected, a simple descriptive interpretation is provided.
A profile of elevated phytanic acid, low-normal pristanic acid, and normal very long-chain fatty acids is suggestive of Refsum disease (phytanic acid oxidase deficiency); however, serum phytanic acid concentration may also be increased in disorders of peroxisomal biogenesis and should be considered in the differential diagnosis of peroxisomal disorders.
If results are suggestive of hemizygosity for X-linked adrenoleukodystrophy, the calculated value of a discriminating function that more accurately segregates hemizygous individuals from normal controls is included in the report.
Positive test results could be due to a genetic or nongenetic condition. Additional confirmatory testing would be required to differentiate between these causes.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
In rare instances, patients with X-linked adrenoleukodystrophy (X-ALD) may have only minimally elevated values; 15% to 20% of women heterozygous for X-ALD have normal plasma very long-chain fatty acid levels.
False-positive results may occur with nonfasting specimens.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Newborn Screening ACT Sheet [Elevated Lysophosphatidylcholine] X-Linked Adrenoleukodystrophy (X-ALD). American College of Medical Genetics and Genomics; 2023. Revised November 2023. Accessed March 25, 2025. Available at www.acmg.net/PDFLibrary/X-ALD-ACT-Sheet.pdf
2. Moser AB, Kreiter N, Bezman L, et al. Plasma very long chain fatty acid assay in 3,000 peroxisome disease patients and 29,000 controls. Ann Neurol. 1999;45:100-110
3. Turk BR, Theda C, Fatemi A, Moser AB. X-linked adrenoleukodystrophy: Pathology, pathophysiology, diagnostic testing, newborn screening and therapies. Int J Dev Neurosci. 2020;80(1):52-72. doi:10.1002/jdn.10003
4. Waterham HR, Ferdinandusse S, Wanders RJA. Human disorders of peroxisome metabolism and biogenesis. Biochimica et Biophysica Acta. 2016;1863(5):922-933. doi:10.1016/j.bbamcr.2015.11.015
Method Description
Describes how the test is performed and provides a method-specific reference
Acidic hydrolysis is followed by basic hydrolysis and reacidification. Hexane extraction then proceeds to derivatization with pentafluorobenzyl bromide (PFB). Separation and detection of PFB-esters is accomplished by capillary gas chromatography mass spectrometry using electron capture ionization and selected negative ion monitoring. Quantitation is enhanced by the use of stable isotope-labeled internal standards.(Stellard F, ten Brink HJ, Kok RM, et al. Stable isotope dilution analysis of very long chain fatty acids in plasma, urine and amniotic fluid by electron capture negative ion mass fragmentography. Clin Chim Acta. 1990;192:133-144; Rattay TW, Rautenberg M, Sohn AS, et al Defining diagnostic cutoffs in neurological patients for serum very long chain fatty acids (VLCFA) in genetically confirmed X-adrenoleukodystrophy. Sci Rep. 2020;10[1]:15093)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Monday through Friday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location
Indicates the location of the laboratory that performs the test
Fees :
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Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.
CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
82726
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| POX | Fatty Acid Profile, Peroxisomal, S | 43677-4 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 81369 | C22:0 | 30194-5 |
| 7143 | C24:0 | 30195-2 |
| 7137 | C26:0 | 30197-8 |
| 7138 | C24:0/C22:0 | 30196-0 |
| 7139 | C26:0/C22:0 | 30198-6 |
| 7140 | Pristanic Acid | 22761-1 |
| 7141 | Phytanic Acid | 22671-2 |
| 7142 | Pristanic/Phytanic | 30550-8 |
| 7144 | Comment | 48767-8 |