Given that evaluating suspected child maltreatment is a challenging task, we aimed to begin to explore how laboratory test results may assist in its detection. Hence, we have examined biomarker differences between 137 children entering out-of-home care and 126 children living in their own homes. Each child entering Majorcan institutionalized care was randomly matched for gender and age with children living in their homes and the same health area. Concerning basic hematological and biochemical values, children placed in out-of-home care differed significantly from children remaining at home in four distinct ways. Children at care entry had significantly higher eosinophil counts than children at home; and also had significantly lower levels of transaminase, thyroid-stimulating hormone, triglycerides and LDL-Cholesterol than children living at home. Oxidative stress linked to anxiety disorders and underweight are common features found in children at entry into the care system. The present study shows a relationship between some underweight or oxidative stress biomarkers and the risk of entry into out-of-home care. Medical diagnoses require physicians to select and assemble relevant data from all available information. Accordingly, we should consider the implementation of laboratory checkups in order to identify the abused from the non-abused child better.