Xylulose
Overview
Xylulose is a five-carbon ketopentose sugar and key intermediate in the pentose phosphate pathway, primarily measured as xylulose-5-phosphate or its dephosphorylated form in metabolic studies. It plays a critical role in carbohydrate metabolism, nucleotide synthesis, and NADPH production for antioxidant defense and lipid biosynthesis. Elevated urinary xylulose indicates essential fructosuria, a benign metabolic disorder due to aldolase B deficiency, while low levels lack established clinical significance. Clinically, xylulose measurement confirms essential fructosuria diagnosis and differentiates it from more serious fructose metabolism disorders like hereditary fructose intolerance.
Clinical Use Cases
- Diagnosis of essential fructosuria (aldolase B deficiency).
- Evaluation of pentose phosphate pathway disorders.
- Metabolic screening in unexplained reducing sugars in urine.
- Research into carbohydrate metabolism abnormalities.
- Differentiation from hereditary fructose intolerance.
Specimen Types
- Urine (spot or 24-hour collection).
- Plasma or serum (research use).
- Cerebrospinal fluid (rare metabolic studies).
Measurement Methods
- Reducing sugar tests followed by chromatography confirmation.
- High-performance liquid chromatography (HPLC).
- Gas chromatography-mass spectrometry (GC-MS).
- Thin-layer chromatography (TLC).
- Enzymatic assays specific for pentoses.
Test Preparation and Influencing Factors
- Fructose ingestion provokes urinary xylulose excretion.
- No fasting required for routine testing.
- High-carbohydrate meals increase baseline excretion.
- Renal function affects urinary concentration.
- Sample contamination with other reducing sugars causes false positives.
- Antibiotics or preservatives alter urine reducing substances.
Synonyms
- D-Xylulose.
- Xylulose-5-phosphate (phosphorylated form).