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HelpTest Code CHOU Carbohydrate, Urine
Reporting Name
Carbohydrate, UUseful For
Screening for conditions associated with increased excretion of fructose, galactose, and xylose
This test is not recommended as a follow up test for abnormal newborn screening for galactosemia.
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| GALU | Galactose, QN, U | Yes | No |
Testing Algorithm
Testing begins with carbohydrate analysis. If qualitative results are normal or abnormal but not indicative of galactose, testing is complete.
If qualitative results indicate the presence of galactose, then quantitative testing for galactose will be performed at an additional charge.
Method Name
Thin-Layer Chromatography (TLC), Qualitative
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
UrineOrdering Guidance
This test 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.
Specimen Required
Supplies: Urine Tubes, 10 mL (T068)
Container/Tube: Plastic, 10-mL urine tube
Specimen Volume: 5 mL
Collection Instructions: Collect an early-morning (preferred) random urine specimen.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Frozen (preferred) | 21 days | |
| Refrigerated | 21 days |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Special Instructions
Reference Values
Negative
If positive, carbohydrate is identified.
Day(s) Performed
Tuesday
CPT Code Information
84377-Carbohydrate
82760-Galactose (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| CHOU | Carbohydrate, U | 16550-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 9255 | Carbohydrate, U | 16550-6 |
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.
In addition to several other saccharide species, chromatography of urinary saccharides identifies galactose and fructose and is, therefore, useful to screen for inborn errors of galactose and fructose metabolism. Xylose may also be detected in individuals with hereditary pentosuria, a benign trait with high frequency among individuals with Ashkenazi Jewish descent.
Interpretation
An interpretive comment is provided.
Cautions
A number of compounds interfere with the assay and microbial contamination can lead to uninterpretable patterns of urinary saccharides. Retesting is recommended in these cases.
Method Description
The urine is chromatographed on a silica gel thin-layer plate. The sugars are located with naphthoresorcinol spray reagent and are identified by visual comparison with a sugar standard chromatographed on the same plate. If galactose is found, it is quantitated by an enzymatic method.(Prinz W, Meldrum W, Wilkinson L: A simple and rapid thin-layer chromatographic method for the identification of urinary carbohydrates. Clin Chim Acta. 1978;82:229-232; Cowan T, Pasquali M: Laboratory Investigations of Inborn Errors of Metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. Elsevier; 2017:1139-1158)