How long do you test positive on a Covid (Coronavirus) antigen test?

Duration of COVID-19 Antigen Test Positivity

Most people will test positive on a COVID-19 antigen test for approximately 5-10 days after symptom onset, with the majority becoming negative by day 10-14. 1

Timeline of Antigen Test Positivity

Early Phase (Days 1-7)

• Antigen tests have lower sensitivity in the first week after symptom onset (approximately 30% sensitivity for combined IgG/IgM testing at days 1-7) 1
• Viral antigen detection requires higher viral loads to register positive, corresponding to RT-PCR cycle thresholds of ≤30 1
• Testing within the first 5 days of symptoms optimizes antigen test sensitivity (89% sensitivity when tested ≤5 days from symptom onset) 1

Peak Detection Period (Days 5-10)

• Antigen test positivity peaks between days 5-10 after symptom onset 1
• At day 5-9 after symptom onset, approximately 54% of tested individuals remained antigen-positive in one study 2
• The median time from symptom onset to first negative antigen test result is approximately 9 days for spike antigen and 13 days for nucleocapsid antigen 3

Late Phase (Days 10-14)

• Most adults clear detectable antigen by 10-14 days after symptom onset 3
• Beyond two weeks, nucleocapsid antigen titers are rarely positive 3
• At day 5 after symptom onset, 80.2% of symptomatic participants who retested remained antigen-positive during the Omicron BA.1 period 4

Important Clinical Distinctions

Antigen vs. PCR Testing Duration

• Viral RNA by RT-PCR remains detectable much longer (often >19 days and up to 30 days) compared to antigen tests 3
• Detection of viral antigen decreases after 10-20 days post-diagnosis, while RT-PCR can remain positive for 3+ weeks due to detection of viral debris rather than viable virus 1
• Antigen testing is a stronger predictor of actual infectiousness than PCR testing after the first week 3

Factors Affecting Duration of Positivity

Disease Severity:

• Contagiousness lasts an average of 10 days in mild-moderate COVID-19 1
• Can extend to 15 days in severe/critical COVID-19 1
• Immunocompromised patients may remain positive up to 20 days from symptom onset 1

Vaccination Status:

• Previous vaccination (primary series) reduces likelihood of prolonged antigen positivity (adjusted OR = 0.60) 2
• Both previous infection AND vaccination together have the strongest protective effect against prolonged positivity (adjusted OR = 0.17) 2

Symptomatic vs. Asymptomatic:

• Symptomatic infection is more likely to result in prolonged antigen positivity (adjusted OR = 9.63) 2
• Asymptomatic individuals may clear virus more quickly 1

Clinical Implications for Isolation

Test-Based Isolation Strategies:

• A negative antigen test after day 5 can support ending isolation if symptoms are resolving and fever has been absent for ≥24 hours without medications 2
• If testing on days 5-9, a positive result indicates continued potential infectiousness and warrants extended isolation 2
• Nucleocapsid antigen testing is strongly associated with viral culture positivity (relative risk = 7.61) and is a better marker of infectiousness than symptoms or PCR alone 3

Common Pitfalls:

• Do not rely on antigen testing in the first 3-4 days of symptoms due to inadequate sensitivity 1
• A negative antigen test in symptomatic patients with high clinical suspicion should be confirmed with PCR 1
• Certain variants (particularly Omicron BA.2) may not be detectable by some rapid antigen tests, causing false-negative results 1
• Positive antigen tests do not require confirmation due to high specificity (>98%) 1