Dried Blood Spot Test (DBS Test): Overview, Benefits, Procedure & Results

Dried blood spot testing is done mainly in newborns for NBS (newborn screening) to find congenital and inherited metabolic disorders. It's been around for about 20 years. It's a novel way of collecting blood without venipuncture, a needle, or a tube.

It has its origins in the 1960s with newborn screening in paediatrics. Only in the last 15-20 years have clinical practitioners used the dried blood spot card collection for infectious diseases. HIV is the primary infectious disease in which dried blood spot testing is starting to gain prominence.

What is DBS Testing?

Dried Blood Spot testing (DBS) is a type of blood collection that makes the HCV (Hepatitis C virus) testing process easier.

This test includes collecting capillary blood samples from a finger prick on a filter paper and drying them before sending them for clinical testing.

DBS testing can help remove barriers to collecting blood samples for testing, such as difficulty in finding venous access, the requirement to centrifuge blood samples after collection, and more.

Other major applications of DBS testing involve DNA/RNA molecular methods. DBS blood test is now being used to detect:

• Hepatitis B virus
• Antibodies to HBV core antigen
• Antibodies to the Hepatitis C virus
• HCV RNA
• HIV (human immunodeficiency virus)

What are the Benefits of DBS Testing?

The major benefits of dried blood spot testing are:

• You do not need a nurse or somebody trained in taking blood with a needle. You prick the end of your finger and then drop blood onto a special paper known as the DBS card.
• Sample collection is easy because dried samples can be kept at room temperature with a dehumidifier for around two weeks. This provides the ideal setting for storage and shipment.
• DBS can detect HCV RNA (to confirm viremic infection) and HCV antibodies (to screen for previous virus exposure).
• A DBS card can be used to test for other viruses. The availability of tests for various diseases will vary depending on your location.
• It makes testing more accessible to people living in rural and isolated places because these remote communities often don't have persons who can take blood with a needle.

DBS Test Procedure

This procedure aims to provide a standardized protocol for preparing and processing dried blood spots to be subsequently used in immunoassays and molecular techniques. This is accomplished by first transferring capillary blood to a filter card.

The second step is to dry blood spots overnight and to obtain 6-millimeter punches out of the circles of the filter card.

Next, technicians get the illusion of dried blood from the punches. This is done by immersing punches in a buffer on a shaker for four hours. The hemolytic eluates are then freed from debris by centrifugation.

The final step is to analyze the cleared eluates for serological and molecular markers of infections with Hepatitis B, Hepatitis C, and HIV by commercially available immunoassays and molecular techniques.

The idea of using a plot collected on a filter card made of cellulose originated a century ago.

Today, people using this method for the first time frequently struggle because the pre-analytical phase is yet to be standardized for almost all applications of DBS testing, given this background.

Test Results

You will receive one of the following results:

• Negative: There is no evidence of Hepatitis C or HIV infection.
• Detected: HIV or Hepatitis C infection is possible. Any test that shows Hepatitis C or HIV is not conclusive, and a second test is required. Discuss with your healthcare provider.
• Invalid: Invalid test results mean it did not work. In this case, you should have another DBS test, or a conventional test should be performed.
• HCV RNA ≤ 40IU/ml: This means the DBS test for Hepatitis C (RNA) was found positive. But the test could not identify how much virus was present in the sample. This could mean two things: either you have HCV or the result is incorrect and you need another blood test.

DBS testing is generally very accurate. The DBS test for HIV will be accurate about 99 times out of 100 in persons with HIV infection.

However, this test may not be able to identify the HIV virus for up to 12 weeks. This is the window period during which only a few tests can provide a false negative result. This means that even if an individual has HIV, the test result could be negative.

Some tests can also give a false positive result, so the test is positive, but the individual does not have an HIV infection. You need more tests to clarify this.

Limitations of the DBS Test

One of the limitations of DBS is the reduced analytical sensitivity of tests done on DBS compared to serum/plasma because biomarkers can be present at low concentrations during infection. However, statistics reveal DBS has a higher analytical sensitivity than RDT.

Another limitation is the manufacturers' inability to use serological and molecular tests on DBS samples. The pre-analytical stages of laboratory analyses performed on DBS retain a manual character. 

As a result, diagnostic testing on DBS is challenging to integrate into the laboratory workflow. This means DBS testing requires extensive validation in clinical laboratories to ensure the quality of the results.

Despite these limitations, DBS is a clinically useful decentralized sampling method. It can help to improve access to in vitro diagnosis to meet the treatment aim of ending the AIDS epidemic and eliminating viral hepatitis as a public health issue.