[False positive on neonatal screening: C5-carnitin increase in newborns due to pre-labour treatment with cefditoren pivoxil].

The increase in C5-carnitin (C5) quantified by tandem mass spectrometry allows for early detection of isovaleric acidemia (IVA) in newborns. The administration of pro- drugs like cefditoren pivoxil (CFP) composed by pivalic acid esters also causes increases of C5 in blood. This work shows the experience of the Laboratorio de Cribado Neonatal of the Comunidad de Madrid in the newborn screening for IVA. 418.863 newborns have been analyzed and no cases of IVA have been detected, but there were 18 cases of increase of C5 in newborns from mothers treated with CFP before labour. The concentrations of C5 obtained in these cases were comparable to those from cases diagnosed of IVA in other countries. We also studied the concentration of C5 the blood of a patient who was treated with CFP, in whom we observed an elevation which was restored after treatment was finished. CFP is an antibiotic prescribed to pregnant women in Spain and can cause elevation of C5 in blood that can induce to suspect a case of IVA, causing alarm in the newborn family and forcing to a follow-up.