Dried blood spot testing
Encyclopedia
Dried blood spot testing (DBS) is a method of screening for HIV
infection and other conditions using DNA amplification
.
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.
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.
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.
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
infection and other conditions using DNA amplification
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
.
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 GuthrieRobert Guthrie
Dr. Robert Guthrie was an American microbiologist, the first to use dried blood spot testing, which he first did in the 1960's...
in 1963. Neonatal screening for phenylketonuria
Phenylketonuria
Phenylketonuria is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase , rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine...
became nationwide in 1969-70. Since then, Guthrie
Guthrie test
The Guthrie test, also known as the Guthrie bacterial inhibition assay, is a medical test performed on newborn infants to detect phenylketonuria, an inborn error of amino acid metabolism. The test has been widely used throughout North America and Europe as one of the core newborn screening tests...
card samples have been collected routinely from infants in over 20 countries to screen for phenylketonuria and more recently for congenital hypothyroidism
Congenital hypothyroidism
Congenital hypothyroidism is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism...
, sickle cell disorders
Sickle-cell disease
Sickle-cell disease , or sickle-cell anaemia or drepanocytosis, is an autosomal recessive genetic blood disorder with overdominance, characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various...
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
Monoclonal antibodies
Monoclonal antibodies are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell....
, 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 desiccantDesiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....
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
Polysorbate 80
Polysorbate 80 is a nonionic surfactant and emulsifier derived from polyethoxylated sorbitan and oleic acid, and is often used in foods. Polysorbate 80 is a viscous, water-soluble yellow liquid...
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.
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 ELISAELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
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.