What is dry blood spot sampling?

One of my clients recently requested me to explain to her what Dry Blood Spot Sampling (DBS) is.

She had been asked to take her baby for this test. DBS is a form of bio-sampling where blood samples are blotted and dried on filter paper. The dried samples are then transported to a centralised laboratory where they are analysed for presence of particular diseases of interest. This form of testing has gained increased use when determining whether a child has gotten infected with HIV from an infected mother, as was the case for my client.

Dry blood spot sampling has also been used to screen for other diseases, especially metabolic diseases in large populations of neonates. They include phenylketonuria, congenital hypothyroidism and sickle cell disorders. The blood sample is usually from a capillary, obtained from pricking the heel or finger and blotted onto filter paper.

Dried blood spot specimens are collected by applying a few drops of blood onto specially manufactured absorbent filter paper. The blood is allowed to thoroughly saturate the paper and is air-dried for several hours. The 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. They are then transported for analysis in the laboratory.

This testing has helped expand HIV diagnostic services for HIV-infected or exposed 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. Done at six weeks of age, the mother of the infant is able to know whether the child has been infected with HIV or not. The test done on the samples looks for the HIV virus DNA, unlike the common rapid tests that look for HIV antibodies, which all test positive for infants born to HIV positive mothers before 18 months of age, regardless of whether the child is truly infected with HIV virus or not.