In vitro diagnostics, marketed directly to consumers without the involvement of a health care provider are called direct-to-consumer tests, or DTC, which are facilitated through easy-to-collect sample matrices such as dried blood spots (DBS), saliva, or swabs that allow the safe and stable transport of samples via mail. At EUROIMMUN, several of the autoimmunity and infectious portfolio tests, including COVID-19, have been adapted to accommodate DBS technology as an alternative sample matrix in addition to serum and plasma.
Collection of blood samples requires a highly skilled professional, such as phlebotomist. During a pandemic like COVID-19, the need for timely collection of biological specimens, limiting exposure to the medical personnel, and maintaining appropriate conditions for specimen transportation, such as temperature, speed etc., are major challenges.
DBS samples are a suitable sampling alternative to expensive and labor-intensive venous blood collection that can be used for routine antibody testing.1 Although serological tests such as the detection of total immunoglobulin or immunoglobulin subtypes can be performed on a DBS matrix, PCR or antigen tests for COVID cannot be performed on DBS using EUROIMMUN tests.
Several parameters can affect the accuracy of DBS measurement during the pre-analytical phase of sample collection.2 Although DBS has been used for many years, there is no standardized protocol approved for their preparation and processing yet. A standardized pre-analytical phase has been reported only for newborn screening, but not for other DBS testing fields.3
Therefore, the analytical performance of the test can vary depending on the absorbent filter paper grades and their manufacture as well as the methodology used for DBS extraction. The choice of an appropriate collection card is also essential for specific tests. The quality of the sample is subject to sample collection and spotting variations. Ideally, only one blood drop should be collected per DBS sample and care should be taken to avoid touching the filter paper.
Care should also be taken to prevent excessive squeezing of the puncture site which can result in hemolysis of the specimen and affect the results. This occurs when red blood cells rupture under pressure. Patients are recommended to fill at least three complete circles with blood out of five so that tests can include replicates.4 This can become complicated and may be difficult for patients who are non-bleeders.
Subsequently, it is crucial that the blood spots on the DBS cards are completely dried before storage or transportation. A minimum of two to three hours drying time in an open space at room temperature is recommended. However, the drying time can vary on the type of paper and the blood volume collected.3,4
Some biomarker concentrations might vary between whole blood and serum or plasma samples. For example, in assessing Vitamin D, results must be converted to their serum equivalent concentrations to provide clinically meaningful results.1
Furthermore, care should be taken to ensure that the analyte is measurable via DBS testing. For instance, measuring levels of anti-tissue transglutaminase (tTG) antibodies is crucial in the diagnosis of Celiac disease. However, it is not possible to measure this analyte through DBS testing. This is because tTG is abundant in red blood cells. During DBS collection, hemolysis of blood cells can cause release of tTG which then binds to autoantibodies of tTG in the blood resulting in false-negative results.
Overall, DBS technology is a suitable, cost-effective, non-invasive alternative to venous blood collection. However, care should be taken during pre-analytics and post-analytics of DBS collection and in interpreting assay results.1 Patients should also be given specific, easy-to-understand instructions for appropriate sample collection.
References
- Zava TT, Zava DT. Validation of dried blood spot sample modifications to two commercially available COVID-19 IgG antibody immunoassays. Bioanalysis. 2021;13(1):13-28.
- Zakaria R, Allen KJ, Koplin JJ, Roche P, Greaves RF. Advantages and Challenges of Dried Blood Spot Analysis by Mass Spectrometry Across the Total Testing Process. EJIFCC. 2016;27(4):288-317.
- Grüner N, Stambouli O, Ross RS. Dried blood spots–preparing and processing for use in immunoassays and in molecular techniques. J Vis Exp. 2015(97):52619.
- Blood Collection and Handling – Dried Blood Spot (DBS). 2005. Accessed 04/18/2021.
