ZRT’s COVID-19 IgG Dual Antibody test is a highly specific laboratory-based test for the antibodies your body makes in response to an infection with the SARS-CoV-2 virus, which is responsible for the disease known as COVID-19.

Antibody testing is commonly referred to as “serology” testing (a test done in blood serum collected by a blood draw from a vein). To circumvent the need for a venipuncture blood draw in a clinic or blood draw station, ZRT Laboratory has developed a simple and convenient method that allows blood drops to be collected from the fingertip, deposited onto a filter card, dried, and shipped directly to ZRT Laboratory for testing of COVID-19 antibodies. ZRT has shown excellent concordance of COVID 19 IgG antibodies to S1 spike protein and nucleocapsid protein with serum collected by venipuncture and by fingerstick dried blood spots (DBS). The advantage of DBS is that the sample can be collected with health care provider assistance and shipped directly to ZRT Laboratory.

ZRT Laboratory’s dried blood spot COVID-19 IgG dual antibody test assesses IgG antibodies against both the SARS-CoV-2 S1 spike and nucleocapsid proteins. Results are reported separately for the S1 spike and nucleocapsid proteins, which helps confirm true positives and reduce false negatives. The CDC has stated the importance of reflex testing to rule out false positives, and literature shows that the SARS-CoV-2 antibody response against different viral proteins can vary significantly in individuals and at different times in the course of the disease. Unfortunately, most reflex tests (if they are offered) only retest if the first result is positive, which means missed false negative results.

ZRT Laboratory is the first laboratory to provide two separate IgG antibody results for every sample, as we believe this is important for confirmation purposes and due to the variation in antibody responses to the SARS-CoV-2 virus.

Who should test?
  • People who have recently had an infection with SARS-CoV-2 (COVID-19) that was confirmed by PCR (molecular) nasal/mouth swab testing and have had no symptoms for at least 7 days
  • People who have recently had a flu-like respiratory illness that may or may not have been COVID-19 because it was not confirmed by virus testing, and have had no symptoms for at least 7 days
  • People who want to see if they might have been exposed to COVID-19 and carry antibodies to the SARS-CoV-2 virus, but have had few or no symptoms

Note: Patients with an active respiratory infection should not test until at least 20 days after the start of symptoms. During early infection when symptoms are present, the immune system may not be making anti-COVID-19 IgG antibodies in sufficient quantity to be detected by the test.

See our FAQ page for answers to questions you may have regarding our COVID-19 IgG Dual Antibody Test.

How reliable is our test?

There are many serology (antibody) tests currently on the market. Some point-of-care (POC) lateral flow cassette IgM/IgG tests are showing lower sensitivity and specificity than is required for population studies. While lateral flow cassettes are fast, convenient, and can use finger stick blood samples, they produce an unacceptable number of false positives and false negatives for population studies. Serum/plasma testing for COVID-19 antibodies using enzyme linked immunosorbent (ELISA) or chemiluminescent assays has high sensitivity and specificity and allows for simultaneous testing of positive and negative controls run in concert with the patient samples.

An ideal solution for antibody testing combines the simplicity of finger stick blood collection with the high sensitivity and specificity of ELISA to detect a prior COVID-19 infection, which may indicate immunity to future infections. The dried blood spot COVID-19 IgG dual antibody test offered by ZRT is exceptionally sensitive and specific for SARS-CoV-2 IgG antibodies against the viral S1 spike and nucleocapsid proteins. ZRT is a CLIA-certified high complexity testing facility with >17 years’ experience working with dried blood spot, and the COVID-19 dual antibody test was stringently validated in-house as a laboratory-developed test (LDT).

See our Provider Data Sheet for more information on the sensitivity and specificity of our test.

Advantages of blood spot testing over conventional serology tests

ZRT has had extensive expertise in finger stick dried blood spot analysis for over 15 years. The advantages are:

  • Easy to collect – see our sample collection instructions and videos
  • Safe – finger stick DBS collection has been safely performed for decades
  • Stable – there are no requirements for freezing or refrigerating samples for transportation, as DBS samples being tested for SARS-CoV-2 IgG are stable for at-least 30 days across all expected shipping temperatures
  • Sample is visible – unlike molecular (PCR) testing using nasal or mouth swabs, which has shown to have high false negative rates due to improperly collected samples, it is very easy to see blood on filter paper and determine the quality of collection
  • Easy to ship – according to the CDC, DBS are exempt human specimens for shipping purposes
  • Low viral risk for sample handlers – most viruses are not viable once dried, making DBS safer to work with than liquid whole blood or serum, or respiratory or fecal samples. Live virus doesn’t last more than 24 hours on cardboard, resulting in minimal risk to mail carriers and specimen receivers
What do the results mean?

Test results are reported as:

  • Positive – you have likely been exposed to the SARS-CoV-2 virus and your body has developed antibodies in response to the infection, whether or not you experienced symptoms or were sick with COVID-19
  • Negative – the test did not detect antibodies to the SARS-CoV-2 virus, suggesting that you likely have not been exposed to the virus; however, a negative result does not absolutely rule out exposure
  • Indeterminate – you may carry antibodies, but they were not present in sufficient quantity to be detected as a strong positive result on the test. Retesting in 2 weeks may help differentiate an indeterminate result from a true positive or negative.
Additional health testing to help modify risk

ZRT tests many other analytes in blood spot to help you understand your overall health and wellbeing. Hormonal imbalances (estradiol, progesterone, testosterone, cortisol), essential mineral deficiencies (iodine, selenium, zinc, magnesium), vitamin D deficiency, and imbalances in cardiometabolic markers of insulin resistance (insulin, hemoglobin A1c, triglycerides) are all showing a strong link to susceptibility to COVID-19 and disease outcome, including risk for death. Imbalances in these markers, which are detectable in the same blood spots used for COVID-19 IgG testing, are emerging as important risk factors for worse outcomes with COVID-19 infection.

FDA-required disclaimer
  • This test has not been reviewed by the FDA
  • Negative results do not rule out SARS-CoV-2 infection, particularly in those who have been in contact with the virus. Follow-up testing with a molecular diagnostic should be considered to rule out infection in these individuals
  • Results from antibody testing should not be used as the sole basis to diagnose or exclude SARS-CoV-2 infection or to inform infection status
  • Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E


COVID-19 IgG Antibody Test Kit Includes:

COVID-19 IgG (blood spot) (Sample Report)

Reference Information

COVID-19 IgG Provider Data Sheet

COVID-19 IgG Antibody Test FAQ

ZRT Test Directory

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