Volume 26, Issue 3 (July 1981)
The Rehydration and Isolation of Leukocytes from Dried Bloodstains
The extraction of leukocytes from dried bloodstains on a variety of surfaces was explored in terms of percentage of recovery. A glycerol-containing solution produced excellent results for many of the surfaces. The outstanding exception was cotton and related cloths, for which a moderate to good result was obtained with a 2-h incubation at 4°c using human serum. A major factor affecting the yield was the blood's ability to form a fibrin network (clotting). In treated or cadaveric blood, 80 to 100% recoveries could be easily obtained from dried crusts or pellets; in blood obtained from a finger prick, a dried crust or pellet yielded only 10 to 25%. A fibrous network containing a large number of entrapped leukocytes was observed under a microscope. This network was identified as fibrin, which acted to collect the cells. The “fibrinconcentrated” leukocytes may be used directly for testing or they can be released by the action of the enzyme plasmin under carefully controlled conditions. Leukocytes may be concentrated from the extraction solution by centrifugation. This step must be done at acidic pH. Leukocyte yields have been high enough to make sex determinations, polymorphic enzyme typing, and human lymphocyte and surface antigen typing feasible in the future.