A survey of apparent blood volumes and sample geometries among filter paper bloodspot samples submitted for lead screening.

Background: Sample collection instructions for the bloodspot lead screening program conducted by the Nebraska Medical Center recommend continuous application of a single finger-stick blood drop per printed filter paper circle (a volume of approximately 50 microl). In this study, we assessed whether apparent blood volumes and geometries of finger-stick bloodspot samples submitted for lead testing were consistent with collection recommendations.

Methods: Samples were 422 extra bloodspots from 138 patients that were submitted for lead analysis. Using image analysis, apparent blood volumes were computed by comparison of bloodspot areas to bloodspot areas for standards of known volume. Circularity of samples was also assessed by image analysis.

Results: Mean blood volume (25+/-13 microl) was approximately 50% of that needed to fill a printed circle. The distribution of volumes had three local maxima, consistent with bloodspot formation by multiple discrete applications of blood drops of small volumes (17+/-6 microl) rather than by continuous application of blood. Multi-drop samples were also apparent from non-circular geometries.

Conclusions: Bloodspots submitted for lead analysis showed an apparently inherent drop volume of less than 20 microl per drop and the application of multiple drops. Non-ideality of such specimens indicates the need for continuing education of bloodspot collectors.