By Emily Maxson, MD - Aledade Chief Medical Officer
Practices across the country are navigating the murky waters of COVID testing. Many communities are waiting 10-12 days for COVID molecular diagnostic test results, left essentially without any useful diagnostics. Rapid point of care testing would be good for patients, good for public health, and good for practice finances. But PCPs are struggling to tease apart the differences between molecular, antigen and antibody tests, search for accurate data that has not been publicly shared, and then attempt to source sufficient supplies.
Aledade has been investigating all channels, directly with distributors and through Group Purchasing Options (GPO). So far, the going has been tough. Manufacturers are giving preference to practices with existing contracts. Even if practices are part of a GPO, practices must order directly through the manufacturer and there are little to no discounts available.
Here at Aledade, we are working toward a new agreement with a GPO now, which may be able to help facilitate an introduction and expedite the ordering process. Ordering through a GPO may allow practices access to test supplies without some of the onerous contracting elements (such as exclusivity and high volume requirements) that some individual physicians are facing.
There are still only four molecular COVID tests and two antigen tests that have Emergency Use Authorization (EUA) from the FDA AND CLIA-Waived status (in other words, 6 diagnostic tests that can be performed in PCP offices).
Initially, there was a fair amount of skepticism based on false-negative rates for antigen tests (these tests are highly specific and positive results are trustworthy, but this comes at the expense of a higher false-negative rate). However, given the challenges in the testing environment, some more positive emerging data, and the fact that these tests are cheaper to produce (and potentially more widely available), antigen testing may occupy an increasingly important role in the testing strategy.
Point of Care Molecular COVID-19 Tests (nasoropharyngeal swab)
* (Caveat - small numbers, predominantly manufacturer derived)
Point of Care Antigen Tests (nasopharyngeal swab)
You’ll note that I did not include antibody tests in the above tables. Antibody tests are not diagnostic, and (if accurate) provide the answer to a different question - are circulating antibodies detectable in the patient’s blood, indicating that the patient’s body has mounted an immune response to the virus sometime in the past?
The challenge with antibody tests is that they are still of limited utility because of high rates of false positives. In the event of a false-positive antibody test, a patient may be falsely reassured that they have been exposed to and mounted an antibody response against the virus. They could unwittingly expose themselves to danger by relaxing precautions.
For these reasons, the CDC cautions the following:
- It is important to minimize false-positive test results by choosing an assay with high specificity and by testing populations and individuals with an elevated likelihood of previous exposure to SARS-CoV-2. Alternatively, an orthogonal testing algorithm (i.e., employing two independent tests in sequence when the first test yields a positive result) can be used when the expected positive predictive value of a single test is low.
- Antibodies most commonly become detectable 1–3 weeks after symptom onset, at which time evidence suggests that infectiousness likely is greatly decreased and that some degree of immunity from future infection has developed. However, additional data are needed before modifying public health recommendations based on serologic test results, including decisions on discontinuing physical distancing and using personal protective equipment.
The CDC further recommends a specificity of 99.5% or greater to diminish the risk of false positives in a relatively low prevalence area. The following 17 antibody tests are listed by the FDA to have a specificity of 99.5% or greater (please note that there are currently NO point of care antibody tests on the EUA list approved for CLIA waived labs):
- Abbott Architect SARS-CoV-2 IgG
- Assure Tech. Assure COVID-19 IgG/IgM Rapid Test Device (acceptable specificity for IgG only)
- Babson Diagnostics aC19G1
- Beckman Coulter Access SARS-CoV-2 IgG
- Bio-Rad Platelia SARS-CoV-2 Total Ab
- EUROIMMUN SARS-COV-2 ELISA (IgG)
- Hangzhou Biotest Biotech RightSign COVID-19 IgG/IgM Rapid Test Cassette
- Hangzhou Laihe Biotech LYHER Novel Coronavirus (2019-nCoV) IgM/IgG Antibody Combo Test Kit (Colloidal Gold) (acceptable specificity for IgM only)
- Healgen COVID-19 IgG/IgM Rapid Test Cassette (acceptable specificity for IgM only)
- InBios SCoV-2 Detect IgG ELISA
- Mount Sinai Hospital Clinical Laboratory COVID-19 ELISA Antibody Test
- Ortho-Clinical Diagnostics VITROS Anti-SARS-CoV-2 IgG test
- Roche Elecsys Anti-SARS-CoV-2
- Siemens Healthcare Diagnostics ADVIA Centaur SARS-CoV-2 Total (COV2T)
- Siemens Healthcare Diagnostics Atellica IM SARS-CoV-2 Total (COV2T)
- Siemens Healthcare Diagnostics Dimension EXL SARS-CoV-2 Total antibody assay (CV2T)
- Siemens Healthcare Diagnostics Dimension Vista SARS-CoV-2 Total antibody assay (COV2T)
In closing, we are taking the testing limitations experienced by practices across the country very seriously and remain committed to helping however we can. To all of our primary care heroes fighting this pandemic on the front lines, please stay safe, and thank you, as always, for continuing to support your communities.