Haematocrit The major assumption in the quantification of data from a dried blood spot is that the blood is uniformly absorbed throughout the body of the spot on the paper. Furthermore, it had been assumed that all blood samples had the same absorption characteristics for cards of the same material. If this were true, then the removal of a fixed diameter disk from a blood spot would remove a fixed volume of blood to enable drug levels to be reproducibly quantified. Unfortunately, the size of the spot produced is controlled by the haematocrit level (or erythrocyte volume fraction) in the blood, which can vary quite considerably – especially for newborns. As the haematocrit level increases, the same volume of blood takes up less space, meaning that the disk sample contains more blood and a subsequent bias in the level of drug detected.

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About the Authors

Sangeeta Tanna

Sangeeta Tanna holds a PhD in pharmaceutics in the development of an artificial pancreas. Her expertise and research interests lie in the bioanalysis and drug delivery fields. This has led to the development of micro-analytical methodologies for the determination of therapeutic drugs from dried blood spots (DBS) based on LC-MS and LC-MS/MS studies for a range of clinical applications. This research was awarded the Royal Society of Chemistry Analytical Methods Prize in 2010. Applications of this work to patient care include improved medication for babies and people with cardiovascular diseases.

Graham Lawson

Graham Lawson’s expertise is instrumental analysis in such disparate areas as environmental exposure in the polymer industry, the identification of migrants from food packaging and factors influencing drug delivery in clinical applications. The unifying themes are the detection of ultra low levels of contamination and the protection of people from adverse exposures. He was co-opted onto a NATO special studies group on the Stand-off detection of radiation. His current research interests include novel analytical techniques applied to blood spot analyses and to counterfeit drug detection.