Dried blood spot testing (DBS) is a form of biosampling where blood samples are blotted and dried on filter paper. The dried samples can easily be shipped to an analytical laboratory and analysed using various methods such as DNA amplification or HPLC.
History
The concept that capillary blood, obtained from pricking the heel or finger and blotted onto filter paper, could be
used to screen for metabolic diseases 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 have been collected routinely from infants 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.
This type of blood testing is now available for use at home by consumers in the U.S. Available blood tests include
vitamin D, estrogen, testosterone, cortisol, TSH and lipids. New York is the only state that prohibits home blood
spot testing.
Procedure
Dried blood spot specimens are collected by applying a few drops of blood, drawn by lancet from the finger, heel or
toe, onto specially manufactured absorbent filter paper. The blood is allowed to thoroughly saturate the paper and
is air dried for several hours.[Specimens are stored in low gas-permeability plastic bags with desiccant added 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 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.
As an alternative to punching out a paper disc, recent automation solutions extract the sample by flushing an
eluent through the filter without punching it out.
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-antibodies 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.
Principle
The reason for stability of DNA, RNA or protein could be attributed to the fact that the biological material binds to
the matrix of the filter paper and the process of drying excludes water which is an important factor necessary for
protease or nuclease to act. Binding of the biological material also binds several inhibitors which may interfere with
various nucleic acid amplification methods.
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