Dried blood spot testing is a diagnostic process that uses drops of blood on a piece of filter paper to test for biological markers of interest. This article summarizes two systematic reviews on the accuracy of dried blood spot testing for screening and confirmatory testing of hepatitis C.1,2 Dried blood spot testing is a simple process and does not need a trained healthcare worker to collect the blood via finger prick.
What is dried blood spot testing?
Dried blood spot testing is a testing process that uses drops of dried blood on a piece of filter paper. It is a simpler process than testing using blood plasma or serum drawn from a vein by a needle in a number of ways. In dried blood spot testing, blood is collected through a finger prick or a heel prick in infants. A lower volume of blood is needed, blood transport and storage are simpler, and less equipment is required.
How is hepatitis C diagnosed?
It takes two different tests to determine whether someone has a hepatitis C infection. The first test is a screening test called the hepatitis C antibody test. It tests to see if someone has ever had hepatitis C. The second test is a confirmatory test. It tests to see if the hepatitis C virus is currently in the body by looking for hepatitis C genetic material (RNA). When using dried blood spot testing, both tests can be performed on the same samples of blood collected on the card.
What kind of research do the systematic reviews include?
Two related systematic reviews examined the accuracy of dried blood spot testing for hepatitis C compared to testing using blood plasma or serum drawn from veins. One review focused on the hepatitis C antibody screening test, the first step in the testing process. The second review focused on the confirmatory hepatitis C RNA test.
The reviews also examined tests used in the diagnosis of hepatitis B; however, this summary will only focus on the results from the hepatitis C tests.
Hepatitis C antibody testing
Twenty-three studies were included in the hepatitis C antibody testing review. A study was included if it collected dried blood spot samples and blood plasma or serum samples for hepatitis C antibody testing. The authors rated the methodological quality of the studies as moderate.
Characteristics of the studies included:
- Published between 1997 and 2017
- Sixteen studies from either Europe, North American or Australia; four from South America; and three from south-east and central Asia
- Limited information provided on participant characteristics with one study including children
Hepatitis C RNA testing
Fifteen studies were included in the hepatitis C RNA testing review, which updated an earlier review covering studies to 2013.3 A study was included if it compared dried blood spot samples and blood plasma or serum samples for hepatitis C RNA testing. The authors rated the methodological quality of the studies as low.
Characteristics of the studies included:
- Published between 1998 and 2015
- Eight studies from Europe, two studies from the United States, two studies from South America; two studies from Asia; and one study from Africa
- Limited information provided on participant characteristics, with three studies among people who inject drugs
How was the accuracy of dried blood spot testing assessed?
The review reported on the sensitivity and specificity of dried blood spot testing in relation to testing with vein-drawn blood plasma or serum. Sensitivity is the percentage of results that will be correctly identified as positive when hepatitis C antibodies or RNA are actually present. Specificity is the percentage of results that will be correctly identified negative when hepatitis C antibodies or RNA are not present.
The review also considered the impact of dried blood spot storage conditions on test accuracy. Storage conditions included storage temperature and length of time in storage.
Is dried blood spot testing accurate when testing for hepatitis C antibodies and hepatitis C RNA?
Hepatitis C antibody testing
The diagnostic performance of dried blood spot testing for hepatitis C antibodies was based on 19 studies. The review found that:
- Sensitivity estimates ranged from 70% to 100%. The pooled estimate determined by combining study results was 98%, indicating high accuracy for the identification of blood samples positive for hepatitis C antibodies.
- Specificity estimates ranged from 95% to 100%. The pooled estimate determined by combining study results was 99%, indicating high accuracy for identification of blood samples negative for hepatitis C antibodies.
The impact of storage conditions on test accuracy was only reported in four of the 19 studies:
- Two studies reported that samples were not stable when stored at room temperature.
- In contrast, two studies found blood samples were relatively stable at room temperature for up to 60 days. These studies also found that storage at temperatures of –20 degrees Celsius produced less variation in results.
Hepatitis C RNA testing
The diagnostic performance of dried blood spot testing for hepatitis C RNA was based on 10 studies. The review found that:
- Sensitivity estimates ranged from 80% to 100%. The pooled estimate determined by combining study results was 98%, indicating high accuracy for the identification of blood samples positive for hepatitis C RNA.
- Specificity estimates ranged from 94% to 100%. The pooled estimate determined by combining study results was 98%, indicating high accuracy for the identification of blood samples negative for hepatitis C RNA.
The impact of storage conditions on test accuracy was reported in six of the studies. Storage at room temperature was not observed to impact test accuracy, although two studies found that RNA levels decreased over time. In contrast, two other studies did not find a decrease in hepatitis C RNA levels in dried blood spot samples after more than 11 months of storage at room temperature.
What are the implications of the review for service providers?
This systematic review found that dried blood spot testing is an accurate way to test for hepatitis C antibodies and hepatitis C RNA. While dried blood spot testing is not currently widely used in Canada, for service providers interested in the potential of dried blood testing, some things to consider include:
- For dried blood spot testing to become more widely available, public health labs will need standardized and validated tests for use with this collection method.
- Dried blood spots are simple and easy to collect and do not require trained healthcare professionals to conduct the testing. Samples can be collected by staff members or volunteers trained in the collection method.
- Testing can easily be conducted in lower resource areas or outside clinical settings because, compared to standard testing, less equipment is required, a lower volume of blood is needed, and transportation and storage of samples is simpler.
- These advantages mean that dried blood spot testing can be used to improve the availability of hepatitis C testing. Dried blood spot testing in settings such as substance use clinics and prisons has been found to improve the frequency of testing in people at high risk for hepatitis C.4
When considering this review, it is important to remember that:
- The review did not include studies in languages other than English or data that was unpublished. The review on hepatitis C RNA testing was also based on a small number of studies. A broader range of settings and procedures may add additional insight into the assessment of dried blood spot testing for hepatitis C.
- The authors caution that the pooled sensitivity estimate of 98% and the pooled specificity estimate of 99% for hepatitis C antibody testing may be overestimated due to variations in the cut-off points used in the studies to determine whether a test was positive or negative.
What is a systematic review?
Systematic reviews are important tools for informing evidence-based programming. A systematic review is a critical summary of the available evidence on a specific topic. It uses a rigorous process to identify all the studies related to a specific research question. Relevant studies can then be assessed for quality and their results summarized to identify and present key findings and limitations. If studies within a systematic review contain numerical data, this data can be combined in strategic ways to calculate summary (“pooled”) estimates. Combining data to produce pooled estimates can provide a better overall picture of the topic being studied. The process of pooling estimates from different studies is also referred to as a meta-analysis.
- Lange B, Cohn J, Roberts T, et al. Diagnostic accuracy of serological diagnosis of hepatitis C and B using dried blood spot samples (DBS): two systematic reviews and meta-analyses. BMC Infectious Diseases. 2017;17(Suppl 1):700. Available from: https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-017-2777-y
- Lange B, Roberts T, Cohn J, Greenman J, Camp J, Ishizaki A, et al. Diagnostic accuracy of detection and quantification of HBV-DNA and HCV-RNA using dried blood spot (DBS) samples – a systematic review and meta-analysis. BMC Infectious Diseases. 2017;17(Suppl 1):693. Available from: https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-017-2776-z
- Greenman J, Roberts T, Cohn J, Messac L. Dried blood spot in the genotyping, quantification and storage of HCV RNA: a systematic literature review. Journal of Viral Hepatitis. 2015 Apr;22(4):353–361. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4409077/
- Coats JT, Dillon JF. The effect of introducing point-of-care or dried blood spot analysis on the uptake of hepatitis C virus testing in high-risk populations: A systematic review of the literature. International Journal of Drug Policy. 2015 Nov;26(11):1050–1055
About the author(s)
Erica Lee is Manager, Website Content and Evaluation at CATIE. Since earning her Master of Information Studies, Erica has worked in the health library field, supporting the information needs of frontline service providers and service users. Before joining CATIE, Erica worked as the Librarian at the AIDS Committee of Toronto (ACT).