Expanding access to infectious diseases testing with dried blood spots and the cobas® Plasma Separation Card

• Dried blood spots (DBS) and the cobas® Plasma Separation Card (PSC) offer alternative blood sampling methods to overcome logistical challenges of traditional venipuncture for infectious disease testing, especially in resource-limited settings
• These techniques can improve access to testing by enabling easier sample collection (like finger-prick), removing cold-chain needs, and maintaining stability at room temperature for easier transport to labs
• The PSC produces a dried plasma specimen with improved RNA stability and is approved for use with the cobas® HIV-1 and cobas® HCV viral load tests, showing similar clinical performance to traditional sample collection methods

Diagnosis of infectious diseases, whether through nucleic acid amplification tests (NAATs) or immunoassays, typically relies on testing plasma or serum samples obtained by venipuncture, which is considered the "gold standard." However, this traditional method poses significant challenges, especially in resource-limited settings, remote areas, or among marginalized populations, even in high-income countries.

The logistical barriers include the need for trained phlebotomists, specialized equipment such as centrifuges, and strict requirements for cold-chain storage and transportation to maintain sample integrity. These obstacles greatly limit access to essential diagnostic testing and monitoring, hindering efforts to control and eliminate diseases such as HIV, viral hepatitis, and other sexually transmitted infections (STIs). The infrastructure demands mean that many regions, particularly in low- and middle-income countries (LMICs), struggle to meet these requirements, creating a significant obstacle to achieving global health goals.

To address these challenges, dried blood spots (DBS) and the cobas Plasma Separation Card (PSC) from Roche are attractive alternative sampling methods. Both DBS and PSC provide a less invasive and more patient-friendly method for collecting samples, often using capillary blood obtained through a simple finger prick, which can eliminate the need for trained phlebotomists for venous blood draws. This enables self- or peer-collection of samples, increasing testing access for hard-to-reach populations, including people living in remote areas, people who inject drugs (PWID), inmates, and men who have sex with men (MSM).

A key benefit of both methods is the removal of cold-chain transportation requirements because these sample types remain stable at room temperature, making transport to centralized labs safer, easier, and less prone to leakage or breakage. This improved stability across elevated temperatures and humidity levels significantly supports biological sampling in remote and under-resourced settings, allowing for large-scale, repeated sampling in national screening efforts and epidemiological research.

These logistical advantages also lead to potential cost savings by eliminating the need for specialized personnel and cold-chain infrastructure. Despite these benefits, particularly with DBS, there are limitations. Specifically, sample quality can vary depending on the blood collection method and biological factors, such as hematocrit levels, which affect blood spreading and analyte recovery. Additionally, DBS contains potentially interfering components from whole blood, such as red blood cells and lymphocytes. Notably, viral RNA may be prone to degradation if DBS samples are exposed to high temperatures or humidity for extended periods.

While offering many benefits, the PSC stands out by producing a dried plasma specimen, unlike DBS, which relies on whole blood specimens. The PSC features a porous membrane that filters out blood cells, allowing only plasma to pass through and collect on a layer of polyester fleece. This separation is crucial because it reduces the influence of whole-blood components, such as red blood cells and lymphocytes, which can interfere with assays designed for plasma or serum.

The PSC fleece is also infused with an RNA-stabilizing reagent, which helps preserve viral nucleic acids across various temperature and humidity levels, thereby improving RNA stability compared to DBS. Additionally, the PSC features multiple distinct sample collection spots, enabling repeat testing or additional tests from the same card, and supporting simultaneous testing for different pathogens or reflex testing strategies.

Both DBS and PSC are suitable for NAAT (detecting viral RNA or DNA) and serological testing (detecting antibodies or antigens). Notably, the cobas Plasma Separation Card is an approved specimen type for the cobas HIV-1 and cobas HCV viral load tests from Roche. Published studies, involving both Roche cobas® molecular assays and Elecsys® immunoassays (e.g., Elecsys® HIV combi PT, Elecsys® HIV Duo, Elecsys® HBsAg II, Elecsys® Anti-HCV II, Elecsys® Syphilis, Elecsys® Anti-SARS-CoV-2), show that these assays perform well clinically when used with DBS/PSC compared to traditional plasma/serum samples.

For HIV viral load (VL) measurement, PSC has demonstrated high performance with sensitivity ranging from 87.5% to 100% and specificity from 87.9% to 99.3% at the WHO-recommended 1000 copies/mL threshold for treatment failure. PSC also showed a lower rate of upward misclassification (3%) for HIV-1 VL (i.e., mistakenly believing a suppressed patient is failing treatment) compared to many DBS reports (10-15%), mainly because PSC minimizes the contribution of cellular nucleic acids to the viral signal. For HIV Ag/Ab testing, studies have shown 100% sensitivity and 100% specificity for DBS compared to serum samples. DBS is also useful for diagnosing early HIV infections in hard-to-reach populations.

PSC has also shown high comparability for HBV and HCV serology and NAATs. One study reported Anti-HCV sensitivity/specificity of 98.7%/100% and HCV RNA sensitivity/specificity of 100%/100% with PSC compared to plasma, while HBsAg sensitivity was 98.4% with PSC.

During the COVID-19 pandemic, DBS proved useful for antibody detection. Sensitivities of 71-100% and specificities of 99-100% have been reported for antibodies to the nucleocapsid (N) protein, while sensitivities of 96-98% and specificities of 76-100% were observed for antibodies to the spike (S) protein using Elecsys® assays with DBS.

For more information describing the utility of DBS and PSC for NAAT and serology infectious disease testing, visit our resources below.

DBS and PSC serve as valuable alternatives to traditional venipuncture for infectious diseases testing, greatly enhancing accessibility and easing logistical challenges, especially in resource-limited or remote areas. They demonstrate similar clinical performance for many key infectious disease markers, particularly when used with Roche's extensive range of molecular and serological tests. However, each method has specific advantages and limitations that must be considered for different settings. Although there is often a trade-off in analytical sensitivity, the increased access and simplified workflows these methods provide largely justify their adoption. Further research is necessary to validate their use across a broader range of NAAT and serological tests. Ongoing efforts are also needed to refine and standardize collection and processing protocols, ensuring optimal and consistent performance worldwide. Updating policies and guidelines is crucial to fully incorporate DBS and PSC into infectious disease diagnostic strategies.