The coronavirus nasal swab test is a PCR test, which is similar to the direct testing for viruses such as herpes. You swab the area, and transport it to the lab in tubes that contain a bit of "viral transport media" or "universal transport media" (special preservatives), which are the same tubes we use for other viral swabs like herpes and influenza. The lab amplifies the DNA of the virus using a common method abbreviated PCR (polymerase chain reaction) to detect if it is present on the swab or not.
Very recently, the FDA made two huge changes to the PCR testing protocol that makes it much easier to do. One, they allow nasal swabs instead of nasopharyngeal or oropharyngeal swabs, which is easy for the patient to collect rather than requiring me to collect it and use up respirators and face sheilds that I don't have. Second, they have asked labs to accept simple sterile swabs transported in sterile saline rather than only accepting viral tranport media tubes. So now I can just sterile pipette in a little saline into sterile tubes and place the regular collection swab in it to send to the lab on ice. No special kit required.
I am using LabCorp to run the test, one of the major labs in the US and who I use for most other labs I order (blood, urine, everything) because their patient pricing is better than labs run by hospitals. Hospital labs overcharge and are not as efficiently run as dedicated lab corporations. Their website is LabCorp.com.
Direct viral PCR tests do not have a very high accuracy in general - the body is not constantly shedding a huge amount of virus 100% of the time in the nose and throat during an infection. It appears to depend on the day of illness, which is obviously difficult to determine given the variability of symptoms in people.
This "novel coronavirus" infection is new, and the test is new, so accuracy data is just coming out from China. The studies are small, and they are only releasing preliminary data, not finalized studies. There are definitely false positives and false negatives for each of the 3 main types of tests, which vary depending on the day of illness each types of test is used.
The best synthesis of the accuracy data of the PCR test and the two major antibody tests (IgG and IgM) is copied below: (PS IgG testing is JUST coming out now and I have some on order but will not offer them until they have actually arrived).
March 31, 2020
Serologic Tests for SARS-CoV-2: First Steps on a Long Road
Mary E. Wilson, MD reviewing Guo L et al. Clin Infect Dis 2020 Mar 21 Zhao J et al. Clin Infect Dis 2020 Mar 28 Li Z et al. J Med Virol 2020 Feb 27
Serologic tests being developed may aid diagnosis and management of COVID-19 and provide insights into the kinetics of the immune response.
Three teams of investigators are developing serologic tests to answer key questions about SARS-CoV-2. Guo and colleagues looked at the kinetics of immunoglobulin M, (IgM), IgA, and IgG antibody response in infected patients using an enzyme-linked immunosorbent assay (ELISA) based on SARS-CoV-2 viral nucleocapsid protein. The researchers assessed 208 plasma samples from 82 confirmed and 58 probable COVID-19 cases.
Antibodies were found as early as 1 day after the onset of symptoms. IgM ELISA detected more cases than polymerase chain reaction (PCR) on day 5.5 of illness. The combination of IgM ELISA plus PCR detected 98.6% of cases versus 51.9% with a single PCR. During the first 5.5 days, PCR had higher positivity rate than IgM; the reverse was true after day 5.5. No cross reactivity was found with common coronaviruses that cause upper respiratory infections. In a family cluster, PCR-negative family contacts of COVID-19 cases had positive serologic assay, confirming the presence of antibodies in asymptomatic infection.
Zhao and colleagues assessed total antibody, IgM antibody, and IgG antibody against SARS-CoV-2 on serial blood samples collected from 173 patients (median age, 48 years) with PCR-confirmed COVID-19 in Shenzhen, China. Plasma samples were tested using ELISA kits supplied by Beijing Wantai Biological Pharmacy Enterprise Co., Ltd., Beijing, China.
In samples collected during the first 7 days after illness onset, positive rates were 66.7% for PCR and 38.3% for antibody assays. During the second week after illness onset, positive rates were 54.0% for PCR and 89.6% for antibody assays. The combined use of PCR and antibody testing improved identification of positivity through various phases of illness. Increases in antibody levels were not associated with RNA clearance, including in three patients with critical illness. A strong correlation was found between clinical severity and antibody titer more than 2 weeks after illness onset. Total antibody was more sensitive than IgM or IgG antibody.
Li and colleagues developed a lateral flow immunoassay that detects IgM and IgG antibodies simultaneously and can test finger-prick blood, serum, and plasma. The point-of-care test provides results within 15 minutes and requires no special equipment. The assay was tested in six provinces in China on blood samples from 397 PCR-confirmed COVID-19 patients and on 128 negative patients.
Overall sensitivity was 88.7%, and specificity was 90.6%. Several authors were affiliated with the company that developed the test (Jiangsu Medomics Medical Technology Co., Ltd., Nanjing, China).
Note to readers: At the time we reviewed these papers, their publishers noted that they were not in final form and that subsequent changes might be made.