Influence of haematocrit level on the kinetics of blood spreading on thin porous medium during dried blood spot sampling

Dried blood spotting (DBS) is a convenient blood collecting and sampling method which is widely applied in newborn screening and blood analysis. At the moment, the practice is to try to keep the blood within a marked circle in a thin porous filter paper. However, it is not always possible to predict exactly how the blood spot spreads inside the filter papers and it depends on many factors including the properties of the filter papers, blood properties and how the blood is deposited on the filter paper. In this paper, we aim to identify the relationships between the physical properties and the spreading behaviour of blood on a typical DBS filter paper (Whatman 903). Pig’s blood was used to mimic the behaviour of human blood and investigate the spreading/imbibition processes of blood drops on the filter paper. Both top and side views were used to analyse the spreading/imbibition behaviour. The experimental data present the haematocrit effect on the spreading dynamics of blood for dried blood spot sampling. The results obtained prove that the spreading/imbibition time dependences of droplet height, droplet base radius and contact angle are universal function of dimensionless time