A CASE REPORT OF FALSE POSITIVE FERRIC CHLORIDE TEST

Phenylketonuria(PKU) is one among the most well known of the aminoacidurias due to primary or cofactor related defect of the enzyme phenylalanine hydroxylase activity causing accumulation of phenylalanine, phenylketones and phenylamines resulting in mental retardation.Increased level of phenylketones in urine causes permanent green colour by ferric chloride test, a screening test for diagnosis of phenylketonuria. An increased urinary level of metabolites of phenylalanine is one of the criteria for a biochemical diagnosis of classic PKU. Here we report a false positive ferric chloride test in a case leading to diagnosis of phenylketonuria, but negative dinitrophenlyhydrazine test and aminoacid profile within normal limits in tandem mass spectrometry.