COVID-19 Serology testing guidelines for UW Medicine Valley Medical Center Primary Care Clinics

BACKGROUND: A serologic test measuring IgG antibodies against SARS-CoV-2 is now available from LabCorp and orderable in Epic. Because this is a new test for a new disease, it is not known if immunity is conferred by a positive serology and what duration any immunity would have. Over 100 different unvetted COVID-19 serology tests are available in the US. UW cannot vouch for other tests’ performance and VMC providers should avoid interpreting outside COVID-19 serology results. Performing these tests safely and effectively in Primary Care requires that providers and staff have the necessary training and tools for patient selection, test interpretation, and patient education. For safety of our patients and staff during social distancing, patients should only be coming to our clinics and clinic laboratories when those visits are necessary for clinical management.

PROCEDURES

All patients who request this test needs to be offered a telehealth visit with a VMC Primary Care provider.

While we currently recommend against ordering this test routinely, if patients are interested in having the test, the telehealth appointment will be used to determine appropriateness and to educate patients regarding the test interpretation. Patients should be specifically and clearly informed that a positive serology does not guarantee immunity and that all social distancing recommendations from Public Health should still be followed. False positives and negatives may occur. Patients who are immunosuppressed may have a diminished antibody response.

Provider guidelines for patient selection and interpretation are attached. Here is an additional reference to explain the limitation of serologic testing:

Patients MUST be without symptoms for at least 14 days prior to testing.

To ensure safety for our clinic and laboratory staff, VMC requires that patients obtaining the test should be without symptoms for at least 14 days. IgG serology is not indicated for diagnosis of acute infection.

No orders for COVID-19 serology will be accepted at UW-VMC lab draw stations from non-VMC PCPs (including specialists and non-VMC providers).

This is vital because we must have clear documentation in EPIC showing that the patient is beyond the period of quarantine in order to safely allow staff or laboratory personnel to perform phlebotomy. COVID-19 serology testing should not be performed to diagnose an acute infection. Specialists and non-VMC providers who wish to have patients tested may refer patients to schedule a telemedicine appointment with a primary care provider.

Patients optimally should be tested no sooner than 25 days from the initial onset of symptoms.

The median time for seroconversion is 10-14 days, but most patients who seroconvert will do so by 25 days. Waiting for 25 days minimizes the chances of missing seroconversion.