Dried blood spot testing
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Dried blood spot testing (DBS) is a method of screening for HIV infection and other conditions using DNA PCR.
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[edit] History
The concept that capillary whole blood, obtained by heel or fingerprick and blotted onto filter paper, could be used to screen for metabolic disease in large populations of neonates was introduced in Scotland by Robert Guthrie in 1963. Neonatal screening for phenylketonuria became nationwide in 1969-70. Since then, Guthrie card samples from two to nine day old babies have been collected routinely in over 20 countries to screen for phenylketonuria and more recently for congenital hypothyroidism, sickle cell disorders and HIV infection. The limitations of sensitivity and specificity when screening such small volumes of blood restricted the use of dried blood spots for many years, however. Recent advances such as the production of monoclonal antibodies, expression of synthetic proteins, and the introduction of the polymerase chain reaction have overcome many of these problems.[1]
[edit] Procedure
Dried blood spot specimens are collected by applying a few drops of blood, drawn by lancet from the finger or the heel, onto specially manufactured absorbent filter paper. The blood is allowed to thoroughly saturate the paper and is air dried for several hours. [2] Specimens are stored in low gas permeable plastic bags with dessicant to reduce humidity, and may be kept at ambient temperature, even in tropical climates.
Once in the laboratory, technicians separate a small disc of saturated paper from the sheet using a an automated or manual hole punch, dropping the disc into a flat bottomed microtitre plate. The blood is eluted out in phosphate buffered saline containing 0.05% Tween 80 and 0.005% sodium azide, overnight at 4°C. The resultant plate containing the eluates forms the "master" from which dilutions can be made for subsequent testing.[3]
[edit] Dried blood spot testing for HIV infection
The technology holds promise for expanding diagnostic services to HIV-infected infants in resource poor settings due to the samples' longer lifespan with reduced need for refrigeration and the less invasive nature of the test compared with other methods. Unlike ELISA testing for HIV-antibody in the blood, which may be transmitted to infants in pregnancy independently of the virus itself, dried blood spot testing can be used to detect genetic material of the actual virus, thereby avoiding the likelihood of a false positive result. DBS specimens also pose less of a biohazard risk to handlers, and are easier to transport or store than liquid blood specimens. [4]
[edit] See also
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