Labs have been performing lead testing on blood collected from children onto filter paper for several years. I developed a procedure for our GFAA analyzers about four years ago. The test is more challenging for the lab in that it is more time-consuming owing to extraction process, it requires calibrators and controls spotted on filter paper circles and samples are typically run in duplicate (preferably two spots each run a single time). Filter paper extractions cannot be run in the same batch with conventional whole blood samples.
For controls, we use selected patient whole blood samples that have been run several time in the conventional mode. We use commercial blood lead calibratores that we reconstitute with sheep red blood cells rather than water. Once spotted they are stable for several months at room temp protected from airborn contamination. In experiments I have done, I have not seen a significant difference when circles are spotted with 2 drops of a sample compared to one drop, even if the second drop is added up to 30 seconds after the first. Crucial to the collection is that the spot is big enough to punch out a circle and that the blood spot saturates the filter paper over the area of the punch-out.
The advantages of filter paper are oriented to the clinic. The process involves a finger stick and often includes a finger stick hemoglobin test. Once clinic staff is trained and experienced, they usually find filter paper more convenient than microtainers in terms of handling, storing and transporting.
Neil Conway, PhD
Cleveland Department of Public Health
Cleveland Ohio email@example.com