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AACC.org // Clinical Laboratory News // All Articles // Nasopharyngeal Swabs May Be Suitable for Rapid Antigen SARS-CoV-2 Testing

Date: MAY.1.2022  // Source: Clinical Laboratory News

Rapid, antigen-based SARS-CoV-2 tests (RAT) on samples collected via nasal swabs or nasopharyngeal (NP) swabs reliably detect SARS-CoV-2 in symptomatic adults who present within 7 days of symptom onset, a recent study found (J Appl Lab Med 2022; doi:10.1093/jalm/jfac004).

High agreement with real-time reverse transcription (RT) PCR confirmation of positive RAT may remove the need for collecting a second swab for RT-PCR confirmation or testing of variants of concern from positive RAT in this population, the paper added.

The study aimed to determine the accuracy of nasal swabs and NP swabs for nasal collection, as well as the effectiveness of using residual extraction buffer for real-time RT-PCR confirmation of positive RAT (rPan). Ninety-nine individuals had nasal swabs, and 56 had NP. Samples were tested immediately with RAT in individuals’ homes by healthcare providers. The providers added 500 mL of universal transport media to the residual extraction buffer and sent it to the laboratory for SARS-CoV-2 testing via RT-PCR. Parallel throat swabs tested with RT-PCR served as reference comparators.

Sensitivity of nasal samples tested on the RAT using either nasal or NP swabs was similar, 89.0% and 90.2%, respectively. rPan positivity agreement compared with throat RT-PCR was 96.2%. Adding the 500 mL of universal transport media to the residual extraction buffer after testing enabled confirmation of positive RAT results.

Use of NP swabs for nasal SARS-CoV-2 testing may be an important alternative when nasal swabs are in limited supply or when NP swabs are in excess, the researchers wrote.

They noted that their study makes no conclusions about RAT performance among symptomatic patients in hospitals or congregate living facilities, asymptomatic patients, and individuals who have had symptoms for more than 7 days. The study is limited by its use of known COVID-19 patients rather than prospective testing of suspect cases.

Some individuals at high risk for developing type 2 diabetes or cardiovascular disease (CVD) can be identified by determining lipidomic risk via just a single mass spectrometric measurement (PLoS Biol 2022; doi:10.1371/journal.pbio.3001561). Simultaneously measuring lipidomics—dozens of types of fats in the blood—is inexpensive and could extend traditional risk assessment, the researchers wrote.

They integrated genetics, lipidomics, and standard clinical diagnostics to assess future type 2 diabetes risk for 4,067 participants from a large prospective, population-based cohort. By training ridge regression-based machine learning models on the measurements obtained at baseline when the participants were healthy, the researchers computed several risk scores for diabetes and CVD incidence during up to 23 years of follow-up.

The researchers used these scores to stratify the participants into risk groups based on quantification of 184 plasma lipid concentrations. The highest risk group had incidence increases of 164% for type 2 diabetes and 84% for CVD. The lowest risk group had decreases in incidence rates of 77% for type 2 diabetes and 53% for CVD. The average case rates were 13.8% for type 2 diabetes and 22% for CVD.

Notably, lipidomic risk correlated only marginally with polygenic risk, indicating that the lipidome and genetic variants may constitute largely independent risk factors for diabetes and CVD. Risk stratification was improved by adding standard clinical variables to the model, resulting in a case rate of 51% and 53.3% in the highest risk group for type 2 diabetes and CVD, respectively. The participants in the highest risk group showed significantly altered lipidome compositions affecting 167 and 157 lipid species for type 2 diabetes and CVD, respectively.

These results show that cheap and fast mass spectrometry can identify a subset of individuals at high risk for developing type 2 diabetes or CVD years before disease incidence, the researchers said.

A recent study calls into question circulating tumor DNA (ctDNA) in conferring a sense of security about the risk of colorectal cancer recurrence.

ctDNA assays as a colorectal surveillance strategy may not provide advantages over standard imaging combined with carcinoembryonic antigen (CEA) levels when performed according to National Comprehensive Cancer Network guidelines, the study said (JAMA Netw Open 2022; doi:10.1001/jamanetworkopen.2022.1093).

Many oncologists have used ctDNA to watch early-stage and resected stage IV colorectal cancer based on evidence from a Danish prospective clinical trial. It showed ctDNA could have a strong prognostic role in follow-up of stage I–III colorectal cancer.

To further examine ctDNA’s usefulness for this purpose, the researchers conducted a retrospective, single-center cohort study that examined sensitivity of ctDNA, imaging, CEA level measurement, and a combination of imaging plus CEA levels in detecting confirmed recurrence of colorectal disease. The researchers defined a confirmed recurrence as a positive ctDNA test or imaging finding confirmed by biopsy, elevated CEA level, or as subsequent tumor radiographic dynamics.

In the study of 48 patients with resected colon cancer, 15 had disease recurrence determined by imaging. Positive ctDNA findings confirmed disease recurrence in 8 patients; imaging in 9 patients; CEA levels in 3 patients; and combined imaging plus CEA levels in 11 patients. The imaging and CEA measurement method had a better sensitivity of 73.3%, compared to 53.3% for ctDNA. The researchers found no significant difference among the methods in the time to identify disease recurrence, with their median time ranging from 14.3 to 15 months.

An accompanying editorial said the findings “suggest that finding MRD [minimum residual disease] in a subset of patients with colorectal cancer may be both unachievable and—worse—not helpful.”

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