In 2016 a global aim to eliminate viral hepatitis as a public health problem by 2030 was set by the World Health Organization (WHO) (2016). The WHO reported that worldwide death rates attributed to hepatitis B (HBV) or hepatitis C virus (HCV) infections in 2013 were 1.46 million, higher than either HIV infection, tuberculosis or malaria (WHO, 2016). Furthermore, fewer than 5% of people with HBV or HCV infections globally were diagnosed (WHO, 2016). Targets to diagnose people with HBV and HCV were subsequently set by the WHO as follows: 30% by 2020 and 90% by 2030. These WHO targets were escalated by NHS England to be achieved by 2025 (All-Party Parliamentary Group on Liver Health, 2018). However, these aims are underpinned by the need for safe and effective methods of obtaining a diagnostic blood sample.
In the UK, 92% of HCV infection occurs in people who inject drugs (PWID) by sharing infected injecting paraphernalia (Public Health England, 2019). Globally, both mother-to-baby transmission and sharing illegal drug-injecting paraphernalia are each associated with 8% of HCV infections (WHO, 2018). Unsafe infection control practices in lower income countries lead to HCV transmission too. For example, in 2010, 5% of healthcare injections worldwide were given with re-used unsterile equipment, resulting in 315 000 HCV infections (WHO, 2018). Furthermore, the use of unscreened blood transfusions in sub-Saharan Africa, India and Egypt continues to pose a high risk of all blood-borne virus transmission (WHO, 2018).
The practical difficulties in obtaining venous blood samples from people whose veins are damaged as a result of intravenous drug taking, such as collapsed peripheral veins (Ciccarone and Harris, 2015), needle phobia (Rice and Abou-Saleh, 2012; Clements et al, 2015) and concerns about possible iatrogenic vein damage (Clements et al, 2015) have led to the introduction of the dried blood spot (DBS) sample technique in many clinical areas as the default method of blood sample collection. Other clinical areas may continue to use a standard venepuncture technique, but this depends on local commissioning arrangements. Oral fluid swabs can be used to detect HCV antibodies but, because a follow-up blood sample is required to confirm active infection if antibodies are present, this dual test process can take longer to confirm a diagnosis.
The intention is that the DBS sample technique will overcome patient barriers to accepting a test and that the levels of uptake, particularly in clinical environments populated by PWID, will rise. This article will explain what a DBS sample is, how it is collected, and how it can help increase the viral hepatitis test uptake in prisons, drug and alcohol services, and other populations at risk of HBV or HCV infection.
Dried blood spot samples
A DBS sample is obtained by a finger-tip skin puncture using a lancet, then collecting capillary blood onto a filter paper test (see Figure 1). This technique was developed by Ivar Christian Bang in 1913, who tested glucose from a DBS sample (Grüner et al, 2015). The four principal advantages of this technique were first summarised by Chapman in 1924 (Grüner et al, 2015) and these are still relevant today:
The DBS test initially gained popularity in paediatrics, having been developed by Guthrie for phenylketonuria testing in new-born babies (Grüner et al, 2015). The expansion of the DBS test method to the adult population has proven to be particularly helpful when needing to obtain blood samples to test for blood-borne viral infection (McAllister et al, 2014). The DBS method of sample collection is considered advantageous for multiple reasons. Of those individuals who have a history of injecting drugs, many will have sclerosed veins as a result of frequent needle access and the acidic pH of the drug solution injected (Ciccarone and Harris, 2015). The presence of damaged, hardened veins can result in profound difficulties in obtaining venous blood samples, which can discourage people from agreeing to have a blood test (Harris, et al, 2014; Clements et al, 2015). The DBS is capillary blood obtained from a finger-prick and thus is comparatively easier to obtain. The lancets used to obtain the capillary blood have retractable needles that reduce the risk of needle-stick injury to staff. The DBS method requires less skill to undertake so it is easier to teach and theoretically enables a wider range of staff to undertake the procedure (Hickman et al, 2008). Furthermore, the DBS samples do not require refrigerated storage and can be sent in the postal system to the receiving laboratory for analysis.
How to obtain a dried blood spot sample
A DBS sample is collected on a Whatman 903 protein saver card (Whatman 903; Cytiva) marked with five equal sized circles that require filling with blood (see Figure 1).
The following steps are required to successfully collect a DBS sample (Grüner et al, 2015):
Although this is a familiar technique to nurses and healthcare assistants in the context of blood glucose monitoring of people with diabetes, an important difference lies in the volume of blood required. Blood glucose machines typically require 0.3 microlitres to 2 microlitres of blood (Pfützner et al, 2013) in contrast to the DBS sample for blood-borne virus testing, which requires 250 microlitres in total; 50 microlitres per Whatman 903 card circle (Tuaillon et al, 2010; Soulier et al, 2016). It is particularly important for the person taking the DBS sample to select a lancet size that will permit the maximum sample to be obtained. Additionally, it may be necessary to puncture the person's finger more than once to obtain the full sample required.
Laboratory testing processes
Once the Whatman card arrives in the laboratory, the blood is eluted (the process of removing an absorbed substance by washing it with a solvent) into a buffer. Each individual spot can be cut out (or better, each spot is surrounded by perforations such that the spot can be pushed out of the paper) and immersed in a suitable liquid, and left for at least an hour (it is often convenient to do this as an overnight step). At the end of this period, the filter paper is removed and what remains is, in essence, a diluted version of the patient's serum. This solution can be processed in any laboratory test just as serum from a venous blood sample might be.
Because the sample is diluted, the sensitivity of the laboratory assay will be considerably less for a DBS than a venous blood sample. For instance, with serum from venous blood it is possible to detect HCV ribonucleic acid (RNA) down to a level of 12 IU/ml, whereas from a DBS, the lower limit of detection will be around 2500 IU/ml. This reduction in sensitivity has to be borne in mind when interpreting results of a DBS sample. In the example just given, this is not usually a diagnostic problem, as more than 97% of patients with chronic HCV infection will have a viral load in excess of 2500 IU/ml. However, this does mean that DBS samples may not be so useful in the monitoring of response to treatment where viral loads may be very low. Other tests that can be run using DBS samples include those for HBV surface antigen, antibodies to HIV, and syphilis serology.
Discussion
A growing body of evidence is emerging that supports the use of DBS sampling to test for viral hepatitis, particularly among communities of PWID. A cluster randomised controlled trial (RCT) was conducted with six prisons and 22 drug treatment services matched into 14 pairs, with one site in each pair randomly allocated to use DBS testing for 6 months (Hickman et al, 2008). The DBS sampling led to a 14.5% (95% confidence interval (CI) 1.3–28%, P=0.033) increase in HCV test uptake. A further RCT conducted to evaluate the accuracy of a HCV antibody test in saliva compared to blood (Rice and Abou-Saleh, 2012) struggled to recruit participants so the DBS technique was introduced. This measure led to recruitment increasing from 1.2 to 5.5 people per week during 10 weeks of data collection. Although not directly investigating the acceptability of the DBS test, this study demonstrated an increase in test uptake. A clinical audit in a substance misuse clinic in Wales (Craine et al, 2009) measured the change in HCV test uptake when the DBS test method was introduced in May 2007. In the previous year, 35 service users had been tested via a venous blood sample but, in the year audited, 202 people were tested using DBS sampling. The authors acknowledge that although some of the increase in testing rates may be attributable to a raised awareness among the clients and the staff, the six-fold increase is consistent with the technique being more acceptable to the client group. An audit by Abou-Saleh et al (2013) reported that HCV testing activity using venous sampling in a community drug service and a prison over 3 months were 31 tests and 1 test conducted, respectively. Following the introduction of the DBS method, test uptake rose to 513 and 43, respectively.
The first article to examine HCV testing in the context of the implementation of a major government policy (McLeod et al, 2014), namely the Hepatitis C Action Plan for Scotland (Scottish Executive, 2006; Goldberg et al, 2008) analysed data from Scotland's four largest health boards between January 1999 and December 2011. The introduction of DBS testing in the community drug clinics led to a 3-fold increase in HCV test uptake (relative risk (RR) 3.5 P=<.001). A more recent evaluation of the impact of DBS testing in 14 East Midlands prisons, albeit as part of a complex intervention that included the contemporaneous introduction of an opt-out approach, showed that the HCV test uptake in 12 months pre- and post-DBS introduction rose from 1972 to 3440 (Jack et al, 2019).
However, it may not be just the DBS technique that increases viral hepatitis test uptake. Four factors that increased testing were observed by Abou-Saleh et al (2013): the enthusiasm of staff, staff numbers, workload, plus the introduction of nurse testing alongside substance misuse key working sessions in community drug teams. Thus, as subsequently observed by Craine et al (2015), Francis-Graham et al (2019) and Jack et al (2020), considering the contexts in which blood-borne virus test uptake interventions are delivered is important.
Conclusion
Obtaining a blood sample using the DBS method is acceptable to patients and staff and is linked to higher rates of test uptake for HCV. Providing this test to people who may be reluctant to engage with unfamiliar health staff is an important opportunity for substance misuse and prison nurses, in addition to key workers. It is, however, important to remember that a higher volume of blood is required than for a blood glucose sample and this impacts on the size of the lancet required and the number of necessary finger-pricks. Of further important consideration is that a DBS sample taken to assess a patient's response to HCV treatment may give a false negative result due to the reduced sensitivity of this test method. However, assessing more people for viral hepatitis infection and arranging treatment if necessary will support the achievement of the goal to eliminate viral hepatitis in the UK by 2025.