By Mariana Bego
The current pandemic is re-shaping the communicable disease testing landscape. Self-sampling, self-testing and rapid diagnostic tests could soon become the norm. In order to help patients fully understand and manage their self-diagnosis, they will need to have access to comprehensive resources in addition to these tools. Self-diagnosis relies on adequate self-sampling and good rapid tests. Improvements in the quality of self-sampling tests will also help improve capacity for tests to be performed in laboratory settings, as a common obstacle for carrying out large-scale testing is the need for in-person sample collection by trained personnel.
In the 1980s, the concept of diabetic patients sampling their blood at home to assess glucose levels was introduced. The technology continued to improve steadily over the following 20 years and at-home testing has revolutionized the way type 1 diabetes is managed. This has set a reference standard of what is possible when it comes to self-testing.
That said, testing for communicable diseases adds another level of complication. Biological sample collection of potentially infected individuals is labour and resource intensive. Trained staff need to be outfitted with personal protective equipment and the collection has to be done in suitable facilities. When testing for communicable diseases, like COVID-19, bringing vulnerable individuals into a healthcare environment for testing may increase the transmission risk. Large scale, lab-centric sampling is impractical and expensive, especially in low and middle-income countries where healthcare resources are limited. The diagnostic performance of different types of samples acquired by trained personnel versus self-sampling has been evaluated recently and reported in several publications.
A recent article published in Scientific Reports (1) compared COVID-19 serological results from self-sampled capillary blood (finger prick) tests to venepuncture (a blood draw with a needle) samples collected by trained personnel. For this study, 209 matched venous and capillary blood samples were obtained from 39 participants and analysed using a COVID-19 IgG ELISA to detect antibodies against SARS-CoV-2. Most participants (38/39) were able to self-collect an adequate amount of capillary blood (50 microliters or 1/100th of a teaspoon). The authors reported almost identical results when comparing capillary and venous blood samples for the detection of SARS-CoV-2 antibodies by IgG ELISA, even when samples were stored for seven days at room temperature. Results only differed for five samples (all collected from two individual subjects) of the 209 matched samples. In these samples, results were very close to the limit of detection for the assay but could be considered positive for venous collection while being indeterminate for capillary blood.
Capillary blood is stored in special tubes and it can be processed immediately on receipt of samples. For dried-blood spot (DBS) collections, the blood is deposited on special paper cards. The steps needed to process the DBS samples are time consuming, as a piece of the card needs to be manually ‘punched’ out and the blood needs to be extracted or eluted from it. The big advantage of DBS samples over capillary blood tubes is the minimal biohazard risk during transport. The authors reported that their results were not influenced by whether the self-collection was done in a capillary tube or on a DBS card.
In the same vein, a systematic review (2) and meta-analysis recently published in The Lancet evaluated the feasibility of self-sampling for diagnosis of SARS-CoV-2 infection by RT-PCR. The authors analyzed 23 studies including approximately 8,000 nasopharyngeal swabs, 1622 nasal swabs, 6110 saliva samples, 338 throat swabs, and 719 pooled nasal and throat swabs from ~8,000 participants. Using nasopharyngeal swabs as the gold standard, pooled nasal and throat swabs gave the highest sensitivity and predictive value (97% for both), whereas lower sensitivities were achieved by saliva and nasal swabs (86% and 85%, respectively). A much lower sensitivity and predictive value was observed for throat swabs (68% and 75%, respectively). Importantly, whether the pooled nasal and throat swab samples were taken by trained staff or self-collected, results were comparable. The analysis suggests that compared with the gold standard of nasopharyngeal swabs, pooled nasal and throat swabs offered the best alternative for diagnosis of SARS-CoV-2 infection in ambulatory care or for self-sampling.
The authors argue that given the urgent need to increase testing capacity globally, these types of self-collection methods have the potential to positively impact testing strategies and programs. Reliable self-collection and self-testing can help reduce COVID-19 exposure risk by decreasing population movement and importantly, will decrease the burden that sampling and testing puts on resources.
- Brown L, Byrne RL, Fraser A, Owen SI, Cubas-Atienzar AI, Williams CT, Kay GA, Cuevas LE, Fitchett JRA, Fletcher T, Garrod G, Kontogianni K, Krishna S, Menzies S, Planche T, Sainter C, Staines HM, Turtle L, Adams ER. Self-sampling of capillary blood for SARS-CoV-2 serology. Sci Rep 11, 7754. Apr 8 2021. doi: 10.1038/s41598-021-86008-5
- Tsang NNY, So HC, Ng KY, Cowling BJ, Leung GM, Ip DKM. Diagnostic performance of different sampling approaches for SARS-CoV-2 RT-PCR testing: a systematic review and meta-analysis. Lancet Infect Dis. 2021 Apr 2. doi: 10.1016/S1473-3099(21)00146-8