At POC and in lab, 2 new checks on SARS-CoV-2 testing

An adequate supply is another. “Abbott made news because they said they’re going to make 50 million tests a month. But even at that rate it would take six months before they could make enough tests for everyone in the country to be tested just once,” he says.

Orders for proficiency testing will be taken through Jan. 15, 2021. Next year’s shipments for the antigen PT are scheduled for April 12 and Oct. 4.

Some of the CAP’s proficiency testing data collected to date for molecular SARS-CoV-2 testing were reported in a letter published online Aug. 12 in Clinical Infectious Diseases (doi:10.1093/cid/ciaa1199) and written by Dr. Rhoads and other members of the CAP Microbiology Committee. In response to an article on the impact of SARS-CoV-2 viral load on risk of intubation and mortality, they provided caveats to consider when applying published findings regarding cycle threshold values to patient results. One of those caveats: “Ct values can vary significantly between and within methods.”

CAP data from more than 700 laboratories using PT material produced from the same batch revealed that the median Ct values reported by the instruments for different FDA EUA methods varied by as much as 14 cycles, Dr. Rhoads and colleagues wrote. “Within a single test performed on the same instrument, the difference in the median Ct-values for different targets was as high as 3.0 cycles,” they continued. And “within a single gene target for a single method, up to 12.0 cycle differences were seen across all laboratories.” The assay and gene target used by the authors of the article on viral load and intubation and mortality risk, ORF1a detected by the Roche Cobas, “differed by approximately 6.0 cycles across all laboratories responding to the survey,” they said.

They pointed out, too, that many clinical labs are using multiple tests that assess different gene targets for SARS-CoV-2 and are testing on different platforms, both of which add to the potential variability of Ct values produced by a single lab. “The ongoing shortage of commercial testing reagents presents a major obstacle to conducting large research studies comparing testing platforms,” Dr. Rhoads and colleagues wrote.

Dr. Rhoads tells CAP TODAY: “There has been growing interest and research around Ct values and the relevance for PCR testing. So, using the data from laboratories that participated in the nucleic acid proficiency testing, we were able to share that information with the medical community and help to caution infectious disease doctors and laboratories not to over-interpret a Ct value.”

Laboratories that enroll in the Quality Cross Check—SARS-CoV-2 Molecular program, known as COV2Q, receive three noninfectious samples that contain the whole SARS-CoV-2 genome, says Lauren N. Pearson, DO, MPH, chair of the CAP Instrumentation Committee and assistant professor in the Department of Pathology, University of Utah School of Medicine, and director of laboratories, University of Utah Health Sciences Center. They analyze the samples on up to three instruments and report the results, indicating on which instrument a given result was obtained. If a lab has more than three instruments, it can purchase more than one kit. The report labs receive from the CAP tells the lab if its results were correct and provides a peer group result comparison.

The report also lets laboratories know how their own instruments performed in comparison with one another. “It will tell you if your results were identical among the instruments that you reported,” she says. If not, the laboratory has to determine where there is a clinically meaningful difference. “Let’s say I got a negative on my ID Now and a positive on my Cepheid instrument. I would want to know about that. It’s helpful information gained from the use of this kit because it’s a discrepancy I would investigate.”

The kit can be used to help laboratories meet the laboratory accreditation twice yearly requirement to ensure instruments are analyzing the same samples equitably, Dr. Pearson says.

A “nice bonus,” she adds, is that labs can use the QCC in meeting the accreditation program training and competency assessment requirements. “Integrating the samples from this kit into that process is one way to do that.”

Shipments of the QCC kits are spaced between PT events so labs can monitor performance across multiple instruments and still maintain compliance with the 2015 CMS directive that prohibits PT on multiple instruments unless that is how the lab tests patient specimens, Dr. Pearson says. “There’s a defined line between what QCC offers compared with proficiency testing. The results from the QCC challenges do not go to any accrediting agency. They don’t go to CMS.”

With labs having implemented testing on or expanded testing to multiple platforms to meet demand during the pandemic, they “want to be sure, at least qualitatively, that the interpretation of the result for a patient’s specimen is the same, no matter which instrument it’s analyzed on,” Dr. Pearson says. For her, as a lab director, it boils down to three things, she says.

“One, am I putting out comparable patient results regardless of which instrument I put the specimen on? Two, how am I going to most easily meet the accreditation program requirements for inter-instrument comparison? And, three, how do I do this while keeping my staff safe? From my perspective, this kit offers the ability to meet and satisfy all of those concerns.”

Valerie Neff Newitt is a writer in Audubon, Pa. To order SARS-CoV-2 antigen PT (COVAG), Quality Cross Check–SARS-CoV-2 Molecular (COV2Q), or any of the CAP’s other COVID-19-related programs, visit cap.org and select Shop at the top of the page.