Evaluation of factors influencing precision in the analysis of samples taken from blood spots on filter paper.

Dried blood spots (DBS) on filter paper have potential as a collection method in screening for haematinic deficiencies. Factors influencing the volumetric precision of uniform 'centre' punches (6.35 mm diameter) removed from dried blood spots have been evaluated. The volume of blood in each DBS punch (n = 234) was greatly influenced by both sample haematocrit (r = 0.63) and haemoglobin concentration (r = 0.63). The volume in identical punches (n = 57) also differed significantly when measured independently using either 125I human serum albumin or haemoglobin relative to the original blood sample. DBS punch volumes should be predetermined for individual batches of filter paper using the specific analyte of interest.