Reducing substances in urine: a paradigm for changes in a standard test.

Detection of reducing substances in urine has been a standard laboratory procedure for about 50 yr. It is used as a screening test for inborn errors of carbohydrate metabolism. Although the test has poor specificity and most states perform mandatory newborn screening for the common genetic defects, most clinical laboratories still perform this as a reflex test on all pediatric urine samples. We suggest that laboratories should perform this test only at the specific order of a physician and that they should review their test menu frequently to delete tests that no longer have a clinical rationale.