Dried blood spot testing

Dried blood spot testing (DBS) is a method of screening for HIV infection and other conditions using DNA amplification.

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.^[1]

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.^[2] 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.^[1]

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.^[3]

References

1. ^ ^{a b} Parker SP, Cubitt WD (September 1999). "The use of the dried blood spot sample in epidemiological studies". J. Clin. Pathol. 52 (9): 633–9. doi:10.1136/jcp.52.9.633. PMC 501537. PMID 10655983. http://jcp.bmj.com/cgi/pmidlookup?view=long&pmid=10655983. 
2. ^ "Information Sheet: Dried Blood". Guidelines for the Shipment of Dried Blood Spot Specimens. Centers for Disease Control and Prevention: Office of Health and Safety: Biosafety Branch. March 9, 1995. http://www.cdc.gov/od/ohs/biosfty/driblood.htm. 
3. ^ Cassol S, Salas T, Gill MJ, et al. (December 1992). "Stability of dried blood spot specimens for detection of human immunodeficiency virus DNA by polymerase chain reaction". J. Clin. Microbiol. 30 (12): 3039–42. PMC 270585. PMID 1452682. http://jcm.asm.org/cgi/pmidlookup?view=long&pmid=1452682. 

See also

• polymerase chain reaction