Genotyping was based on two blood spot punches of 3.2 mm, equivalent to 6 μl of whole blood.30 Biological components are generally very well preserved in neonatal dried blood spot samples, in particular if the samples are stored at −20 °C. However, it may be challenging to analyse the samples due to the very limited amount of biological material available, the nature of dried whole blood on filter paper and decades of storage. In particular, the determination of concentration of biomarkers in dried blood spots is less precise than in serum. This calculation is based on the assumption that one punch 3.2 mm in diameter is equivalent to 3 μl of whole blood, which only applies if the filter paper is fully and evenly saturated. Moreover, measurements are performed on whole blood containing various cell types that may have an influence on the concentration of certain components. The hematocrit, which is usually unknown, is also an important factor for blood components that do not re-distribute into red blood cells. Special high sensitive assays may be required and multi-analyte measurements are
