Test Id : SAU
Sialic Acid, Free and Total, Random, Urine
Useful For
Suggests clinical disorders or settings where the test may be helpful
Screening for sialic acid disorders
Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request
This is a screening test to detect patients with sialic acid disorders such as free sialic acid storage disorder, sialidosis and galactosialidosis.
Quantitation of free and total sialic acid and the ratio of these are provided.
Method Name
A short description of the method used to perform the test
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/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
Free sialic acid storage disorder
FSASD
Galactosialidosis
Infantile free sialic acid storage disease
ISSD
N-acetylneuraminate pyruvate lyase deficiency
NPL deficiency
Salla disease
Sialic acid disorder
Sialidosis
Sialuria
Specimen Type
Describes the specimen type validated for testing
Urine
Ordering Guidance
This is a recommended screening test for patients suspected to have a diagnosis of free sialic acid storage disease.
Urine oligosaccharides are also recommended for patients with a suspected diagnosis of sialidosis or galactosialidosis.
Necessary Information
Patient's age is required.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Supplies: Sarstedt Aliquot Tube, 5mL (T914)
Container/Tube: Plastic, 5-mL tube
Specimen Volume: 1 mL
Pediatric Volume: 0.5 mL
Collection Instructions: Collect a random urine specimen (early morning preferred).
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.
0.5 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
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 |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 90 days | |
| Frozen | 90 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Screening for sialic acid disorders
Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request
This is a screening test to detect patients with sialic acid disorders such as free sialic acid storage disorder, sialidosis and galactosialidosis.
Quantitation of free and total sialic acid and the ratio of these are provided.
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Sialic acid (SA), or N-acetyl-neuraminic acid, is a component of carbohydrates, glycoproteins, and gangliosides which are important for the human nervous system. SA can be measured in urine as free sialic acid or in a conjugated form, bound to oligosaccharides. Sialic acid disorders are a subset of lysosomal disorders caused by defective protein transport or enzyme deficiency that result in multisystem organ disease. Analysis of free and total sialic acid and their ratio in urine can detect the following conditions: free sialic acid storage disorder, sialuria, N-acetylneuraminate pyruvate lyase (NPL) deficiency, sialidosis, and galactosialidosis.
Free sialic acid storage disorder (FSASD) is a rare lysosomal disorder caused by a defect in sialin, a sialic acid membrane exporter also known as SLC17A5. This defect results in increased stored free sialic acid in the lysosomes. Individuals with FSASD demonstrate the hallmark feature of progressive neurologic issues such as hypotonia, cerebellar ataxia, short stature, and cognitive impairment. Brain imaging may show central hypomyelination, cerebellar atrophy, and thinning of the corpus callosum. Infants and children with more severe disease may also have coarse facial features and organomegaly, such as enlarged liver and heart. A congenital form of the disease has been reported in which patients present with nonimmune hydrops fetalis. Historically, FSASD was divided into several conditions based on early to later age at disease presentation and severity: infantile free sialic acid storage disease, intermediate severe Salla disease, and Salla disease. These conditions are now considered to represent the spectrum of FSASD. There are no approved therapies for FSASD at present. Urine sialic acid analysis will show elevated free sialic acid and a high ratio of free to total sialic acid in individuals with FSASD. FSASD is an autosomal recessive condition caused by disease-causing variants in the SLC17A5 gene.
There are two additional rare disorders that show elevated free sialic acid: sialuria and N-acetylneuraminate pyruvate lyase (NPL) deficiency. Sialuria is an autosomal recessive disorder caused by disease-causing variants in the GNE gene that results in onset of symptoms such as organomegaly and developmental delay in infancy. NPL deficiency is also inherited in an autosomal recessive manner due to pathogenic variants in the NPL gene. Individuals with NPL deficiency develop progressive cardiomyopathy and mild skeletal myopathy in childhood. There are no approved therapies for these conditions, and so treatment is supportive.
Sialidosis is caused by a deficiency of the enzyme neuraminidase which results in accumulation of sialyloligosaccharides in lysosomes. Individuals with sialidosis can present with a continuum of clinical features ranging from severe disease (type II) to a milder and more slowly progressive course (type I). These clinical features range from early developmental delay, coarse facial features, short stature, dysostosis multiplex, and hepatosplenomegaly to late onset cherry-red spot myoclonus syndrome. Seizures, hyperreflexia, and ataxia have been reported in more than 50% of later onset patients. A congenital form of the disease has been reported in which patients present with fetal hydrops or neonatal ascites. Urine sialic acid analysis will show a low ratio of free to total sialic acid in individuals with sialidosis, as they have increased excretion of conjugated SA. Analysis of urine oligosaccharides (OLIGU / Oligosaccharide Screen, Random, Urine) is also recommended for patients with a suspected diagnosis of sialidosis. Sialidosis an autosomal recessive condition caused by disease-causing variants in the NEU1 gene.
Galactosialidosis also presents with a continuum of clinical features ranging from severe and rapidly progressive disease to a milder and more slowly progressive course; clinical features of the early infantile type include fetal hydrops, edema, ascites, visceromegaly, dysostosis multiplex, coarse facies, and cherry red spot(s) in the retina. Most patients have milder presentations, which include ataxia, myoclonus, angiokeratoma, cognitive and neurologic decline. Urine sialic acid will show a low ratio of free to total sialic acid in individuals with galactosialidosis, as they have increased excretion of conjugated SA. Analysis of urine oligosaccharides is also recommended for patients with a suspected diagnosis of galactosialidosis. Galactosialidosis is an autosomal recessive condition caused by disease-causing variants in the CTSA gene.
Patients with an abnormal urine sialic acid result suggestive of any of the sialic acid disorders should have follow up confirmatory testing with the appropriate enzyme or molecular test.
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.
Free Sialic Acid:
< or =4 weeks: < or =208 mmol/mol creatinine
5 weeks-12 months: < or =104 mmol/mol creatinine
13 months-18 years: < or =100 mmol/mol creatinine
> or =19 years: < or =38 mmol/mol creatinine
Total Sialic Acid
< or =4 weeks: < or =852 mmol/mol creatinine
5 weeks-12 months: < or =656 mmol/mol creatinine
13 months-18 years: < or =335 mmol/mol creatinine
> or =19 years: < or =262 mmol/mol creatinine
Total/Free Ratio:
< or =4 weeks: 1.94-18.68
5 weeks-12 months: 2.34-13.85
13 months-18 years: 2.63-9.18
> or =19 years: 3.35-15.81
An interpretive report will also be provided.
Interpretation
Provides information to assist in interpretation of the test results
An elevated result of total/free sialic acid ratio may be indicative of sialidosis or galactosialidosis.
A decreased result of total/free sialic acid ratio may be indicative of free sialic acid storage disorder.
Abnormal results or clinical suspicion should be confirmed with biochemical or molecular genetic analysis.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Mild elevations of urinary free sialic acid may occur due to other causes, including sepsis, renal disease, hemolytic uremic syndrome and type 2 diabetes mellitus.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1.Adams D, Wasserstein M. Free Sialic Acid Storage Disorders. In: Adam MP, Mirzaa GM, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle;1993-2023. Updated January 23, 2020. Accessed June 10, 2025.Available at: www.ncbi.nlm.nih.gov/books/NBK1470/
2. Huizing M, Hackbarth ME, Adams DR, et al. Free sialic acid storage disorder: Progress and promise. Neurosci Lett. 2021;755:135896. doi:10.1016/j.neulet.2021.135896
3. Khan A, Sergi C. Sialidosis: A review of morphology and molecular biology of a rare pediatric disorder. Diagnostics (Basel). 2018;8(2):29. Published 2018 Apr 25. doi:10.3390/diagnostics8020029
4. Annunziata I, d'Azzo A. Galactosialidosis: historic aspects and overview of investigated and emerging treatment options. Expert Opin Orphan Drugs. 2017;5(2):131-141. doi:10.1080/21678707.2016.1266933
Method Description
Describes how the test is performed and provides a method-specific reference
Sialic acid is measured twice to give a free sialic acid and a total sialic acid value.
Free sialic acid is measured by drying down a 10 mcL aliquot from a random urine collection, reconstitution in 3M hydrochloric acid (HCl) in butanol to give the respective butyl ester. The butyl-ester sialic acid is reconstituted in eluent and submitted for liquid chromatography tandem mass spectrometry analysis.
Total sialic acid is measured by hydrolyzing a 10 mcL aliquot from a random urine collection with HCl. The hydrolyzed sialic acid is then converted to the respective butyl ester with 3M HCl in butanol. The butyl ester sialic acid is reconstituted in eluent and submitted for liquid chromatography tandem mass spectrometry analysis.
Both free and total sialic acid is quantitated using a commercially available stable isotope labeled internal standard from calibration over a concentration range 2.0 to 2000 mcM.(Tebani A, Schlemmer D, Imbard A, Rigal O, Porquet D, Benoist JF. Measurement of free and total sialic acid by isotopic dilution liquid chromatography tandem mass spectrometry method. J Chromatogr B Analyt Technol Biomed Life Sci. 2011;879[31]:3694-3699. doi:10.1016/j.jchromb.2011.10.009; Li J, Wu T, Zhang X, Du Y, Wei B, Wang J. Clinical application of liver diseases diagnosis using ultrahigh-sensitive liquid chromatography-mass spectrometry for sialic acids detection. J Chromatogr A. 2022;1666:462837. doi:10.1016/j.chroma.2022.462837)
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.
Thursday
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 :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
- Authorized users can sign in to Test Prices for detailed fee information.
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- Prospective clients should contact their account representative. For assistance, contact Customer Service.
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.
84275
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 |
|---|---|---|
| SAU | Sialic Acid, Free and Total, U | 104657-2 |
| 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.
|
|---|---|---|
| 621069 | Free Sialic Acid | 104658-0 |
| 621070 | Total Sialic Acid | 104659-8 |
| 621071 | Total/Free Sialic Acid Ratio | 104660-6 |
| 621072 | Interpretation | 94423-1 |
| 621073 | Reviewed By | 18771-6 |