Positive ferric chloride test UMLS:C4025589 If positive, the ferric chloride test indicates an increased concentration of phenols in the urine or blood. The ferric chloride test indicates presence of high levels of phenylpyruvate in urine, because ferric ion forms a blue-green colored complex with phenylpyruvate. Some other compounds can also lead to a positive ferric chloride test. The ferric chloride test is no longer used in modern clinical practice, but this term is kept for historical reasons. The urine phenylpyruvate concentration is elevated in phenylketonuria. HP:0003612 Positive FeCl3 test Abnormal circulating phenylalanine concentration