Bloodstain Pattern Analysis (BPA) focuses upon the analysis of the size, shape, and distribution of bloodstains resulting from bloodshed. BPA is calculated by using the flight and stain characteristics of blood as a function of its physical properties, with viscosity being one of the three most important contributing factors.

Craig Banks and Dale Brownson, Manchester Metropolitan University, UK, have studied the effect of amphetamine on the viscosity of blood and the implications for BPA.
A range of relevant amphetamine concentrations were chosen:

• 3.0 X 10^–7 mol dm^–3, taken as a therapeutic blood concentration;
• 9 4.1 X10^–6 mol dm^–3, to represent an average dose;
• 4.1 X 10^–5 and 4.1 X 10^–4 mol dm^–3, believed to be within the fatal range of amphetamine;
• 4.1 X 10^–3 mol dm^–3, above the stated fatal concentration.

Increased amphetamine levels were shown to decrease the viscosity of blood by up to 11 % (4.1 X 10^–3 mol dm^–3). The new values for viscosity did not produce a large variation in stain diameter for a vertical drop of ~6 ft (~1.8 m) (max. 2.9 % alteration, resulting in a 0.61 mm difference in diameter at the highest concentration), however, it had a greater effect when calculating blood impact at an angle. In this case, the difference in viscosity alters the length of a stain and consequently a different angle of impact will be calculated based upon standard trigonometry.

The authors question whether such a small alteration would cause a misinterpretation of evidence, but note that the effect of drugs on blood viscosity should be kept in mind by crime scene investigators.

• Crime scene investigation: The effect of drug contaminated bloodstains on bloodstain pattern analysis
  D. A. C. Brownson, C. E. Banks,
  Anal. Methods 2010, 2.
  DOI: 10.1039/C0AY00537A