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Test Code CHOU Carbohydrate, Urine

Reporting Name

Carbohydrate, U

Useful For

Screening for conditions associated with increased excretion of carbohydrates, including inborn errors of fructose and galactose metabolism.

 

This test is not recommended as a follow up test for abnormal newborn screening for galactosemia.

Testing Algorithm

Qualitative testing for the presence of reducing substances is performed followed by quantitative analysis of carbohydrates including fructose, galactose, xylose, glucose, sucrose, lactose, maltose, and raffinose.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Urine


Ordering Guidance


This test is a quantitative analysis of carbohydrate excretion in the urine. It is not appropriate for evaluation of an abnormal newborn screen for galactosemia. For those cases, order GCT / Galactosemia Reflex, Blood and consider GAL1P / Galactose-1-Phosphate, Erythrocytes and GATOL / Galactitol, Quantitative, Urine.



Necessary Information


Patient's age is required.



Specimen Required


Supplies: Urine Tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 5 mL

Collection Instructions:

1. Collect an early-morning (preferred) random urine specimen.

2. No preservative.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Frozen 42 days

Reference Values

Reducing Substances: Negative

 

Quantitative results are reported as mmol/mol creatinine.

Age range

<12 months

12 months-18 years

≥19 years

Xylose

≤13

≤38

≤9

Fructose

≤32

≤31

≤16

Galactose

≤117

≤32

≤5

Glucose

≤139

≤15

≤22

Sucrose

≤27

≤46

≤20

Lactose

≤160

≤18

≤5

Maltose

≤5

≤1

≤2

Raffinose

≤1

≤1

≤1

Day(s) Performed

Tuesday

Test Classification

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

84379

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CHOU Carbohydrate, U 74447-4

 

Result ID Test Result Name Result LOINC Value
622708 Interpretation 59462-2
622709 Reducing Substances 5809-9
622710 Xylose 75051-3
622711 Fructose 34309-5
622712 Galactose 25102-5
622713 Glucose 34312-9
622714 Sucrose 76132-0
622715 Lactose 74438-3
622716 Maltose 74895-4
622717 Raffinose 48147-3
622744 Reviewed By 18771-6

Clinical Information

Carbohydrates are a group of mono-, di-, and oligosaccharides of endogenous and exogenous sources. Their presence frequently reflects dietary consumption but can indicate specific pathology if either a particular saccharide or a particular excretory pattern is present. Most saccharides (except glucose) have low renal thresholds and are readily excreted in the urine.

 

The identification and quantitation of carbohydrates, in particular galactose and fructose, is useful to screen for inborn errors of galactose and fructose metabolism such as galactosemia and hereditary fructose intolerance. Additionally, xylose may also be detected in individuals with hereditary pentosuria, a benign trait with high frequency among individuals with Ashkenazi Jewish ancestry.

 

This test is useful as an initial screen. To establish any diagnosis, abnormal results require confirmation by enzyme assay, molecular genetic analysis, or correlation with other laboratory testing.

Interpretation

When abnormal results are detected, a detailed interpretation is given, including an overview of the results and of their significance, a correlation to available clinical information, elements of differential diagnosis, recommendations, if any, for additional biochemical testing, and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.

Cautions

Ingestion of sorbose, a naturally occurring ketohexose,(1) will interfere with the quantitation of fructose and an interference comment will be included in the report. Retesting is recommended in these cases.

 

In some instances, normal carbohydrate values for infants (<12 months) and pediatric patients can result in a positive result for reducing substances. This is due to higher normal excretion of carbohydrates in younger age groups.

Clinical Reference

1. Hastings J, Owen G, Dekker A, et al. ChEBI in 2016: Improved services and an expanding collection of metabolites. Nucleic Acids Res. 2016;44(D1):D1214-D1219. doi:10.1093/nar/gkv1031

2. Steinmann B, Gitzelmann R, Van den Berghe G. Disorders of fructose metabolism. In: Valle DL, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA. eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill Education; 2019. Accessed February 21, 2025. https://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225080452

3. OMIM. #260800 Pentosuria; PNTSU. Johns Hopkins University; 1986. Updated July 9, 2016. Accessed February 21, 2025. Available at https://omim.org/entry/260800

4. Gaughan S, Ayres L, Baker P II. Hereditary fructose intolerance. In: Adam MP, Feldman J, Mirzaa GM, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2015. Updated February 18, 2021. Accessed February 21, 2025. Available at www.ncbi.nlm.nih.gov/books/NBK333439

Method Description

The urine is evaluated for reducing substances using the AimTab tablet (Benedict's test). The tablet is a standardized self-heating method for the determination of the reducing substances by copper reduction.

 

Urine is spiked with a mixture of labeled internal standards and evaporated. The dry residue is oximated, derivatized, then extracted. Specimens are analyzed by gas chromatography mass spectrometry, selected ion monitoring using positive ammonia chemical ionization and stable isotope dilution.(Unpublished Mayo method)

Report Available

3 to 9 days

Specimen Retention Time

2 months

Reject Due To

Urine containing preservatives Reject

Method Name

Gas Chromatography Mass Spectrometry (GC-MS)

Secondary ID

9255