What is the process for ordering Covid antibody testing for a patient?

How to Order COVID-19 Antibody Testing

COVID-19 antibody testing should be ordered through your laboratory's standard serology ordering system, specifying SARS-CoV-2 IgG and/or IgM antibody testing, but understand that antibody tests are NOT recommended for diagnosing acute COVID-19 infection—they detect past exposure or immune response after infection or vaccination. 1

When Antibody Testing Is Appropriate

Valid Clinical Indications:

• Determining past SARS-CoV-2 exposure in patients who were never tested during acute illness but have clinical history suggesting prior COVID-19 2, 3
• Assessing immune response after vaccination or documented infection for research or epidemiological purposes 4, 3
• Seroprevalence studies at the population level to evaluate community exposure rates 3
• Evaluating cellular immunity when combined with T-cell assays (ELISpot) in patients with suspected prior infection but no detectable antibodies 3

When NOT to Order Antibody Testing:

• Never use antibody tests to diagnose acute COVID-19 in symptomatic patients—antigen or NAAT testing is required instead 1
• Do not use antibody tests to screen for active infection before procedures or hospital admission 1
• Avoid using antibody tests to determine immunity status for workplace screening, as the correlation with protective immunity remains unclear 1, 3

Practical Ordering Process

Step 1: Select the Appropriate Test Type

• ELISA or chemiluminescence immunoassays (CLIA) offer higher sensitivity (96% for IgG) and specificity (98%) compared to rapid lateral flow tests 5
• Laboratory-based testing is preferred over point-of-care rapid tests for clinical decision-making due to superior performance characteristics 3, 5
• Specify IgG testing as the primary target, since IgM has lower sensitivity (15-70%) and adds limited clinical value 5

Step 2: Order Through Your Laboratory System

• Use standard serology order codes such as "SARS-CoV-2 antibody, IgG" or "COVID-19 serology panel" depending on your institution's nomenclature 4
• Collect serum or plasma samples using standard venipuncture technique—whole blood can be used for point-of-care tests but is less reliable 5
• Ensure at least 14-21 days have elapsed since symptom onset or exposure, as antibody sensitivity is low in the first week and peaks after 2-3 weeks 2, 6

Step 3: Interpret Results with Critical Caveats

Positive Antibody Result:

• Indicates past SARS-CoV-2 exposure through infection or vaccination, not necessarily current infection 2, 3
• Does not confirm protective immunity or predict protection against reinfection 3
• May reflect cross-reactivity with other coronaviruses, particularly in patients with autoimmune disease, though specificity is generally high (98%) 6, 5

Negative Antibody Result:

• Does not rule out past infection, as some patients never develop detectable antibodies or antibody levels wane over time 6, 3
• Consider T-cell testing (ELISpot) if clinical suspicion for prior infection remains high despite negative serology 3
• May occur in immunocompromised patients who mount inadequate humoral responses 6

Critical Pitfalls to Avoid

• Do not order antibody tests for acute diagnosis—this is the most common misuse; symptomatic patients require antigen or NAAT testing within 5 days of symptom onset 1, 7
• Do not assume positive antibodies equal immunity—the correlation between antibody levels and protection against infection or severe disease is not established 3
• Do not test too early—antibody tests have poor sensitivity (<50%) in the first week after exposure and should be delayed until at least 14 days post-symptom onset 2, 6
• Do not use rapid point-of-care tests for clinical decisions when laboratory-based ELISA/CLIA is available, as rapid tests have significantly lower sensitivity (85-87% vs. 96%) 5
• Do not interpret negative antibody results as definitive absence of prior infection—cellular immunity may be present without detectable antibodies 3