Benzene Derivatives from Ink Lead to False Positive Results in Neonatal Hyperphenylalaninemia Screening with Ninhydrin Fluorometric Method

Abstract

Ninhydrin-based fluorometric quantification of phenylalanine is one of the most widely used methods for hyperphenylalaninemia (HPA) screening in neonates due to its high sensitivity, high accuracy, and low cost. Here we report an increase of false positive cases in neonatal HPA screening with this method, caused by contamination of blood specimen collection devices during the printing process. Through multiple steps of verification, the contaminants were identified from ink circles printed on the collection devices to indicate the positions and sizes of blood drops. Blood specimens from HPA-negative persons collected on these contaminated collection devices showed positive results in the fluorometric tests, but negative results in tandem mass spectroscopy (MS/MS) experiments. Contaminants on the collection devices could be extracted by 80% ethanol and showed an absorption peak around 245 nm, suggesting that these contaminants may contain benzene derivatives with similar structure to phenylalanine. High-performance liquid chromatography (HPLC) analysis of the ethanol extracts from contaminated collection devices identified two prominent peaks specifically from the devices. Methyl-2-benzoylbenzoate (MBB, CAS#606-28-0) was found as one of the major chemicals from contaminated collection devices. This report aims to remind colleagues in the field of this potential contamination and call for tighter regulation and quality control of specimen collection devices.