SARS-CoV-2 Antigen

Bacterial/ Viral

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Rapid antigen test.

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SARS-CoV-2 Antigen Test Information Guide

Why is it done?
- Detects viral proteins (antigens) from SARS-CoV-2 in respiratory samples to diagnose acute COVID-19 infection
- Rapid screening for symptomatic individuals with suspected COVID-19 infection
- Identification of infectious individuals to guide isolation and treatment decisions
- Mass screening in healthcare settings, workplaces, schools, and community settings
- Pre-travel or pre-procedure screening to reduce transmission risk
- Assessment of close contacts or household members exposed to confirmed COVID-19 cases
- Most commonly performed within 5-7 days of symptom onset when viral load is typically highest
Normal Range
- Result Interpretation: • Negative: No SARS-CoV-2 antigen detected (normal/expected result)
- Positive: SARS-CoV-2 antigen detected (abnormal/indicative of infection)
- Invalid: Test result cannot be interpreted (usually due to technical error or improper sample collection)
Units of Measurement:
- Qualitative test (Positive/Negative/Invalid) - not a quantitative measurement
- Some laboratory-based antigen tests may report semi-quantitative optical density (OD) values, but clinical reporting is typically binary
Interpretation:
- Negative result indicates absence of SARS-CoV-2 antigen in the sample; individual is presumed not to have active COVID-19 at time of testing
- Positive result confirms current SARS-CoV-2 infection and indicates the person is potentially infectious
Interpretation
- Positive Result:
  - Indicates active SARS-CoV-2 infection with detection of viral antigens in respiratory tract
  - Person should be isolated to prevent transmission to others
  - May warrant initiation of antiviral therapy (paxlovid, remdesivir) depending on risk factors and timing
  - Positive results have high specificity (95-99%) but moderate sensitivity (40-90% depending on test type and viral load)
- Negative Result:
  - No SARS-CoV-2 antigen detected in the sample
  - Does not rule out infection if symptoms are present early in illness (pre-peak viral shedding) or if sample quality is poor
  - Symptomatic individuals with negative antigen test may require confirmatory molecular testing (RT-PCR)
- Factors Affecting Results:
  - Timing of test - sensitivity highest 2-7 days after symptom onset
  - Quality of sample collection - improper or insufficient specimen may yield false negatives
  - Specimen type - nasopharyngeal and oropharyngeal swabs generally more sensitive than nasal or saliva samples
  - Viral variant - some tests may have variable performance with emerging variants
  - Immunocompromised status - may have prolonged shedding or variable antigen levels
  - Vaccination status - does not directly affect test accuracy but may correlate with illness severity
- Clinical Significance:
  - Positive test provides rapid confirmation of COVID-19 and justifies immediate isolation measures
  - Guides antiviral treatment decisions and contact tracing protocols
  - More sensitive than nucleic acid amplification tests (NAATs) in high viral load situations but less sensitive overall
Associated Organs
- Primary Organ Systems Affected:
  - Respiratory system (primary site of viral replication and detection)
  - Upper respiratory tract - nasal passages, nasopharynx, oropharynx
  - Lower respiratory tract - trachea, bronchi, lungs (in severe cases)
- Associated Medical Conditions:
  - COVID-19 (Coronavirus Disease 2019) - the primary diagnosis confirmed by positive test
  - Acute respiratory infection with symptoms of cough, fever, dyspnea, or sore throat
  - Pneumonia - viral pneumonia with potential for rapid progression
  - Acute respiratory distress syndrome (ARDS) - in severe cases
  - Bronchitis - inflammation of bronchial tubes
- Systemic Complications:
  - Cardiovascular - myocarditis, thromboembolism, cardiac arrhythmias
  - Renal - acute kidney injury from severe infection
  - Hepatic - elevated liver enzymes and potential acute liver dysfunction
  - Hematologic - coagulopathy and thrombocytopenia in severe COVID-19
  - Neurological - anosmia, dysgeusia, encephalopathy in severe cases
  - Post-COVID syndrome (long COVID) - persistent symptoms weeks to months after acute infection
- High-Risk Groups for Severe Disease:
  - Elderly individuals (age >65 years)
  - Immunocompromised patients (organ transplant recipients, HIV/AIDS, chemotherapy)
  - Chronic medical conditions (diabetes, heart disease, respiratory disease, obesity)
  - Pregnant individuals
Follow-up Tests
- Confirmatory Testing:
  - SARS-CoV-2 RT-PCR (nucleic acid amplification test) - gold standard for confirmation if antigen test is negative but clinical suspicion high
  - SARS-CoV-2 serology/antibody testing - to assess immune response or past infection history (not for acute diagnosis)
  - Repeat antigen test 24-48 hours later if initially negative but symptoms persist
- Diagnostic Support Testing:
  - Chest X-ray or CT imaging - to assess for pneumonia or lung involvement in symptomatic patients
  - Oxygen saturation monitoring (pulse oximetry) - to assess respiratory function
  - Arterial or venous blood gas analysis - for severe respiratory cases
- Laboratory Studies for Severity Assessment:
  - Complete blood count (CBC) - assess for lymphopenia and thrombocytopenia
  - Comprehensive metabolic panel (CMP) - evaluate kidney function, liver function, electrolytes
  - D-dimer and prothrombin time (PT/INR) - to assess for coagulopathy in severe cases
  - Inflammatory markers (CRP, procalcitonin, ferritin) - to assess severity and predict complications
  - Troponin and BNP - if myocardial injury or heart failure suspected
- Monitoring Recommendations:
  - Asymptomatic close contacts should undergo follow-up antigen or molecular testing on day 5-7 after exposure
  - Resolution testing is NOT recommended - antigen and molecular tests may remain positive for weeks
  - Hospitalized patients may require serial laboratory monitoring every 24-48 hours
  - Post-COVID syndrome evaluation if symptoms persist >4 weeks after initial infection
Fasting Required?
- Fasting Status: No - Fasting is NOT required for SARS-CoV-2 antigen testing
Patient Preparation:
- No special dietary restrictions required
- No medications need to be held prior to testing
- Avoid eating, drinking, smoking, or chewing gum 30 minutes before nasopharyngeal or oropharyngeal swabbing (may affect sample quality)
Sample Collection Instructions:
- Nasopharyngeal or oropharyngeal specimens are preferred for optimal sensitivity
- Swabs must be collected using appropriate sterile collection kits specified by the testing laboratory
- Samples must be processed and tested within the time frame specified by the kit manufacturer (typically 24-48 hours)
- Proper specimen labeling and chain of custody must be maintained
Medications and Interfering Substances:
- No medications interfere with antigen detection
- Recent nasal saline or steroid nasal sprays should be noted but do not contraindicate testing
- Antiviral medications (paxlovid, remdesivir) should not be used before testing as they may reduce viral antigen levels

How our test process works!