The aim of this study is to test a screening strategy directly targeting vitamin B12 deficiency together with inborn cobalamin disorders such as CblC, D. Based on published data on elevated homocysteine values in newborns with vitamin B12 deficiency, we recently started to determine homocysteine concentrations after increased propionylcarnitine in Austrian newborns’ dried blood spot samples using tandem mass spectrometry. The gene discussed is CBLC; the disease is vitamin B12 deficiency.