Diagnostic Tests and Procedures Practice Test

The test is designed to detect a metabolic disorder called phenylketonuria in newborns by looking for phenylketones in urine. In PKU, a deficiency in the enzyme that converts phenylalanine to tyrosine leads to buildup of phenylalanine and its byproducts, including phenylketones, which appear in urine. Finding these metabolites early is crucial because, with prompt dietary management that limits phenylalanine, the risk of intellectual disability and other neurological problems can be greatly reduced. The other tests listed don’t screen for metabolic disorders through urinary phenylketones: a potassium test gauges electrolytes, PSA screens for prostate cancer, and proctosigmoidoscopy examines the lower bowel.