When is the best time to test for COVID-19 (Coronavirus Disease 2019)?

Optimal Timing for COVID-19 Testing

For symptomatic individuals, the best time to test for COVID-19 is within the first 5 days of symptom onset, with testing as soon as symptoms appear being optimal for early detection and treatment. 1

Testing Guidelines Based on Symptoms Status

For Symptomatic Individuals:

• Test as soon as symptoms develop for optimal detection and early treatment initiation 1
• Use NAAT (PCR) testing when available with timely results (within 1 day) 1
• If NAAT results would be delayed >1 day, use rapid antigen testing instead 1
• Antigen tests perform best within the first 5 days of symptoms (89% sensitivity) 1
• After 5 days from symptom onset, test sensitivity decreases significantly to 54% 1

For Asymptomatic Individuals with Known Exposure:

• Test at least 5 days after exposure to COVID-19 1
• If symptoms develop before day 5, test immediately 1
• A single antigen test can be used in specific situations where results will impact subsequent actions 1

Test Selection and Interpretation

Test Type Considerations:

• NAAT (PCR) testing is the most sensitive option (fewer false negatives) 1
• Antigen tests have high specificity (≥98%) but lower sensitivity (81% overall, 89% within 5 days of symptoms) 1
• A positive result from either test type can be trusted without confirmation due to high specificity 2

Negative Test Results:

• If using antigen test and clinical suspicion remains high, confirm with NAAT 1
• Routine repeat testing after a negative NAAT is not recommended 1
• If repeat testing is needed, perform 24-48 hours after initial testing 1, 2

Common Pitfalls to Avoid

1. Delayed Testing: Testing too late (>5 days after symptom onset) significantly reduces test sensitivity 1
2. Unnecessary Repeat Testing: Routine repeat testing after negative NAAT results is not recommended and strains healthcare resources 1, 2
3. Misinterpreting Persistent Positivity: Positive tests 3+ weeks after infection likely represent non-infectious viral shedding rather than ongoing infectiousness 2
4. Ignoring Pre-test Probability: Clinical suspicion should guide interpretation of negative results, especially with antigen tests 1
5. Poor Specimen Collection: Inadequate sample collection can lead to false negatives 1

Special Considerations

• Self-collected specimens (anterior nasal or mid-turbinate) perform similarly to healthcare provider-collected specimens 1
• Saliva specimens have high sensitivity (92%) and may be a good alternative to nasal swabs 1
• Early diagnosis through appropriate testing timing has been shown to decrease transmission, particularly in school settings 3
• Day-7 testing after exposure can identify approximately 3% of asymptomatic cases 4

By following these evidence-based guidelines for COVID-19 testing timing, clinicians can optimize detection, facilitate early treatment, and help prevent transmission while avoiding unnecessary testing.