Measurement of Hematocrit in Dried Blood Spots Using Near-Infrared Spectroscopy: Robust, Fast, and Nondestructive

o the Editor: Dried blood spot (DBS)1 collection is an established sampling method for new born screening and is increasingly used in other domains, including therapeutic drug monitoring, toxicology, microbiology, and genetics. Advantages of DBS sampling are the low blood volume requirements, minimally invasive collection, favorable stability of many analytes, and the potential of patient self-sampling at home. Importantly, the introduction of more sensitive techniques in the clinical laboratory has paved the way for analysis of small volume DBS samples in clinical chemistry (1). A well-recognized concern for accurate analyte quantification using DBS is the hematocrit (Ht) effect (2). First, Ht influences blood viscosity and thereby fluidity of blood on the paper. This can lead to different volumes of blood in equally sized punches and to varying analyte concentrations within the spot, resulting in a potential bias. Second, Ht may influence analyte extraction from the paper. Third, many analytes in clinical chemistry are currently measured in plasma and/or serum, whereas DBS samples are whole blood lysates. Therefore, for many compounds, Ht is necessary to accurately convert DBS measurements to plasma/serum values. Previously proposed techniques to …