Incidence and causes of positive tests for reducing substances in urine of children

Background: Inborn errors of metabolism is a general term applied to numerous genetic disorders pathology of which is usually attributed to excessive tissue storage or abnormally high circulating concentrations of a specific not degraded metabolic substance. Early diagnosis can prevent irreversible complications of some of these disorders. Errors in carbohydrate metabolism belong to this category of disturbances. Sugars of clinical interest are all reducing sugars. The aim of this study was determination of the incidence rate and causes of positive Benedict's test in hospitalized or outpatient children under 14 years of age. In addition, identification of interfering substances that could cause false positive results and the necessity of Benedict's test prior to chromatography were other purposes of the study.
Methods: 1473 urine samples in a case series and prospective study were examined. Benedict's test was done for detection of reducing substances and paper chromatography for identification of the specific reducing sugar and amino acids present in the urine.
Findings: 59% of the samples were positive for reducing substances. Significant decrease in positive results was occurred with restricted diet (free of fruits, vitamin C, honey, drugs). Paper chromatography for sugars and amino acids were performed on positive samples. Lactose was the most frequently found (32%) sugar followed by galactose (24%). In 54% there were no reducing sugars detected. The results also showed 36% cystein and 19% other amino acids in positive samples. No significant differences were observed in rate and degree of positive results with respect to sex and age of the patients.
Conclusion: The results obtained in this study indicate that important reducing sugars or amino acids may be detected even in weakly positive results of Benedict's test, thus justifying follow-up studies of positive test for reducing substances in urine.

Keywords
Reducing substances , amino acid , reducing sugars , chromatography and Benedict's test