Test Catalog

Test Id : SSCTU

S-Sulfocysteine Panel, Urine

Useful For
Suggests clinical disorders or settings where the test may be helpful

Diagnosis of molybdenum cofactor deficiency, isolated sulfite oxidase deficiency, and hereditary xanthinuria


Monitoring patients with molybdenum cofactor deficiency or isolated sulfite oxidase deficiency who are on treatment


This test provides a quantitative report of S-sulfocysteine, xanthine, hypoxanthine, and uric acid in urine identified via liquid chromatography-mass spectrometry.

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

S-Sulfocysteine Panel, U

Lists additional common names for a test, as an aid in searching



Uric Acid


Hereditary xanthinuria

Isolated sulfite oxidase deficiency

Lesch-Nyhan syndrome

Molybdenum cofactor deficiency

Xanthine dehydrogenase and xanthine aldehyde oxidase dual deficiency

Xanthine dehydrogenase deficiency

Xanthine dehydrogenase/xanthine aldehyde oxidase/sulfite oxidase combined deficiency

Specimen Type
Describes the specimen type validated for testing


Ordering Guidance

This is the recommended test when clinical features are suggestive of, or when molecular testing results suggest, molybdenum cofactor deficiency, isolated sulfite oxidase deficiency, and hereditary xanthinuria. This test includes measurement of relevant purines in addition to urine S-sulfocysteine and uric acid. If the clinical features are suggestive of a purine and pyrimidine metabolism disorder or are nonspecific, order PUPYU / Purine and Pyrimidines Panel, Random, Urine.


This test will be canceled if ordered with PUPYU.

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: Urine Tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 3 mL

Collection Instructions: Collect a random urine specimen.


Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

2 mL

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

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 Frozen 90 days

Useful For
Suggests clinical disorders or settings where the test may be helpful

Diagnosis of molybdenum cofactor deficiency, isolated sulfite oxidase deficiency, and hereditary xanthinuria


Monitoring patients with molybdenum cofactor deficiency or isolated sulfite oxidase deficiency who are on treatment

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Urine S-sulfocysteine is elevated in 2 disorders with similar clinical phenotypes, molybdenum cofactor deficiency (MoCD) and isolated sulfite oxidase deficiency. Molybdenum is an important trace element that is biosynthesized into an important cofactor, which is essential for the proper functioning of the enzymes, xanthine oxidase, sulfite oxidase, and aldehyde oxidase in addition to nitrogenases and nitrate reductase. Four genes are important in mediating the biosynthetic pathway to create molybdenum cofactor, MOCS1, MOCS2, MOCS3, and GPHN (gephyrin). The 3 clinical types of MoCD are autosomal recessive diseases resulting from 2 disease-causing variants in the respective causative gene. MoCDs result in a progressive neurodegenerative disease that manifests with seizures and brain abnormalities in the first weeks to months of life. The most common type of MoCD is MoCD A, caused by variants in MOCS1 and resulting in neonatal or infantile onset seizures and postnatal encephalopathy with rapidly progressive neurodegeneration. Infants with MoCD B (MOCS2 or MOCS3), and C (GPHN) have all been reported but are rare. Infants with MoCD have increased S-sulfocysteine and hypoxanthine and decreased uric acid concentrations in urine. The treatment for MoCD A only is cyclic pyranopterin monophosphate infusion and is most effective when initiated early.


Isolated sulfite oxidase deficiency (ISOD) is an autosomal recessive disorder caused by deficiency of the enzyme sulfite oxidase, which results in progressive neurodegenerative disease in most cases. ISOD is the result of disease-causing variants in the SUOX gene. ISOD is a spectrum of disease ranging from severe, early onset disease that appears in the first days of life with seizures, feeding issues, and neurologic issues causing abnormal muscle tone, to mild, later onset disease manifesting after 6 months of age with developmental delay or regression, movement issues, which can be episodic, and ectopia lentis in some cases. Infants with ISOD have increased S-sulfocysteine and normal hypoxanthine concentrations in urine. Treatment is largely symptomatic, with medication for seizures and movement/neurologic issues. Unfortunately, no treatment for the underlying metabolic defect is currently available. Prevalence is unknown, but ISOD is likely underdiagnosed.


Hereditary xanthinuria results in kidney stones and, less commonly, muscle pain and cramping caused by accumulation of xanthine that forms crystals in the kidneys and muscle tissue. There are 2 types of hereditary xanthinuria: type I caused by deficiency of xanthine dehydrogenase resulting from disease-causing variants in the XDH gene, and type II caused by deficiency of molybdenum cofactor sulfurase resulting from variants in the MOCOS gene. Individuals with xanthinuria have increased xanthine and decreased uric acid concentrations in urine. The incidence of both types of hereditary xanthinuria is about 1 in 69,000 individuals.

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.


0-3 years

4-6 years

7-12 years

13-18 years

>18 years


< or =65

< or =30

< or =30

< or =30

< or =30


< or =54

< or =21

< or =35

< or =15

< or =20

Uric Acid







< or =11

< or =5

< or =5

< or =5

< or =5


All results reported as mmol/mol creatinine

Provides information to assist in interpretation of the test results

Abnormal concentrations of measurable compounds will be reported along with an interpretation. The interpretation of an abnormal metabolite pattern includes an overview of the results and of their significance, a correlation to available clinical information, possible differential diagnosis, recommendations for additional biochemical testing and confirmatory studies (enzyme assay, molecular analysis), name, and phone number of contacts who may provide these studies, and a phone number of the laboratory directors in case the referring physician has additional questions.

Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Additional confirmatory testing via enzyme assays and molecular genetic testing is required for follow-up of abnormal results.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

1. Melcher K, Mountford WK, Hoffmann GF, Ries M: Ultra-orphan diseases: a quantitative analysis of the natural history of molybdenum cofactor deficiency. Gen Med. 2015 Dec;17(12):965-970

2. Claerhout H, Witters P, Regal L, et al: Isolated sulfite oxidase deficiency. J Inherit Metab Dis. 2018 Jan;41(1):101-108

3. Misko AL, Liang Y, Kohl JB, Eichler F: Delineating the phenotypic spectrum of sulfite oxidase and molybdenum cofactor deficiency. Neurol Genet. 2020 Jul 14;6(4):e486

Method Description
Describes how the test is performed and provides a method-specific reference

Diluted, filtered urine is mixed with an internal standard mixture and analyzed for hypoxanthine, xanthine, uric acid and S-sulfocysteine by liquid chromatography-tandem mass spectrometry. The ratios of the extracted peak areas of the purine and pyrimidine analytes to the added internal standards are used to calculate the concentration of purines and pyrimidines present in the sample.(la Marca G, Casetta B, Malvagia S, et al: Implementing tandem mass spectrometry as a routine tool for characterizing the complete purine and pyrimidine metabolic profile in urine samples. J Mass Spectrom. 2006 Nov;41(11):1442-1452; Rashed MS, Saadallah AAA, Rahbeeni Z, et al: Determination of urinary S-sulphocysteine, xanthine and hypoxanthine by liquid chromatography-electrospray tandem mass spectrometry. Biomed Chromatogr. 2005 Apr;19(3):223-230; Monostori P, Klinke G, Hauke J, et al: Extended diagnosis of purine and pyrimidine disorders from urine: LC MS/MS assay development and clinical validation. PLoS One. 2019 Feb 28;14(2):e0212458. doi: 10.1371/journal.pone.0212458)

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.

Tuesday, 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.

3 to 7 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

1 month

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


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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. This test 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.


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
SSCTU S-Sulfocysteine Panel, U 94397-7
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.
607007 Interpretation (SSCTU) 59462-2
607002 Hypoxanthine 38366-1
607003 Xanthine 38371-1
607004 Uric Acid 34385-5
607005 S-Sulfocysteine 33876-4
607006 Reviewed By 18771-6

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports