Semicarbazide is a non-reliable marker in spray-dried red blood cells for nitrofurazone abuse

Semicarbazide (SEM) is a metabolite of the antibiotic nitrofurazone. Its presence in animal derived products is used as an indicator that an animal was illicitly treated with the antibiotic. The use of nitrofurazone in food-producing animals in the EU was banned in 1993 because of its carcinogenicity. Hence, a minimum required performance limit (MRPL) of 1 mu g/kg SEM was established by EU legislation (Commission Decision 2003/181/ EC). A new regulation applies an even lower Reference Point for Action (RPA) of 0.5 mu g/kg for all nitrofurans and their metabolites from November 2022 (Commission Regulation (EU) 2019/1871). However, SEM can be formed from other precursors not just nitrofurazone. Processing-related SEM residues have been detected in protein-rich foods such as milk or egg powder, gelatin, and carrageenan after drying and storage. The objectives of this study were to evaluate whether SEM is formed in porcine red blood cells (RBC) throughout drying and storage. Furthermore, the role of urea, a common metabolite naturally present in blood, as potential precursor to SEM was to be investigated. Total SEM was determined after acidic hydrolysis and derivatization by liquid chromatography-tandem mass spectrometry (LC-MS/MS). SEM was not detected in liquid RBC but was quanti-fiable after spray drying or lyophilization of liquid RBC. The addition of 1 and 5 g/kg urea to liquid RBC before drying resulted in increased levels of SEM in the dried product. The addition of urease to the liquid RBC reduced the level of SEM in the spray-dried product. Finally, SEM levels increased in commercially produced spray-dried RBC during storage under ambient warehouse conditions. These results indicate that SEM should not be used as an indicator of previous illicit treatment with nitrofurazone in RBC.