What ICD-10 codes are used to rule out flu and COVID-19?

ICD-10 Codes for Ruling Out Influenza and COVID-19

When evaluating patients to rule out influenza and COVID-19, use ICD-10 code Z03.818 (encounter for observation for suspected exposure to other biological agents ruled out) or Z20.828 (contact with and suspected exposure to other viral communicable diseases) for exposure scenarios, and use specific symptom codes (such as R05.9 for cough, R50.9 for fever) combined with the appropriate "rule out" documentation until diagnostic testing confirms or excludes these infections.

Primary ICD-10 Codes for Rule-Out Scenarios

For Suspected COVID-19

• Z03.818: Encounter for observation for suspected exposure to other biological agents ruled out 1
• Z20.828: Contact with and (suspected) exposure to other viral communicable diseases - use when patient has known or suspected exposure to COVID-19 1
• U07.1: COVID-19, confirmed - only use after positive RT-PCR or other confirmatory testing 1
• U07.2: COVID-19, virus not identified - use when provider documents "suspected," "possible," or "probable" COVID-19 but not confirmed by testing 1

For Suspected Influenza

• Z20.828: Contact with and (suspected) exposure to other viral communicable diseases 1
• J09.X2-J11.1: Use specific influenza codes only after confirmation with rapid antigen or PCR testing 2

Clinical Context for Code Selection

When to Use Exposure Codes

The Infectious Diseases Society of America defines exposure requiring documentation as close contact for at least 15 minutes over a 24-hour period with someone who has laboratory-confirmed COVID-19, or working/residing in congregate settings experiencing outbreaks 1. For these scenarios:

• Document Z20.828 when the exposed individual tests negative or test results are unknown 1
• Testing should occur at least 5 days after exposure, or immediately if symptoms develop before 5 days 1

When to Use Symptom-Based Codes

Until diagnostic testing confirms or excludes infection, code the presenting symptoms:

• R05.9: Cough, unspecified - cough has 62.4% sensitivity for COVID-19 3
• R50.9: Fever, unspecified - fever has 37.6% sensitivity for COVID-19 3
• R43.0: Anosmia (loss of smell) - anosmia has 94.2% specificity for COVID-19 3
• R43.2: Parageusia (altered taste/ageusia) - ageusia has 92.6% specificity for COVID-19 3
• R06.02: Shortness of breath 3
• R53.83: Fatigue 3

Diagnostic Testing Requirements for Code Assignment

COVID-19 Testing

The Infectious Diseases Society of America recommends SARS-CoV-2 RNA testing (RT-PCR) as the reference standard, with sensitivity of 92% for saliva specimens and specificity of 98% 1. Code assignment depends on test results:

• Positive RT-PCR: Use U07.1 (COVID-19, confirmed) 1
• Negative RT-PCR with high clinical suspicion: Consider repeat testing 24-48 hours later before ruling out; continue using symptom codes 1
• Asymptomatic positive: Use U07.1 with documentation of asymptomatic status 1

Influenza Testing

Rapid antigen testing provides quick screening but has high false-negative rates; RT-PCR is the gold standard for viral identification 2. Use specific influenza codes (J09.X2-J11.1) only after confirmation 2.

Key Clinical Differentiators Affecting Code Selection

Features More Suggestive of COVID-19

• Anosmia or ageusia (positive likelihood ratio 4.55 and 3.14 respectively) 3
• Age 15-70 years, breathing difficulty, malaise 4
• Longer hospital stays and higher mortality 5
• Ground-glass opacities on chest imaging with peripheral distribution 6

Features More Suggestive of Influenza

• Upper respiratory symptoms (sore throat has negative likelihood ratio 0.814 for COVID-19) 3
• Body temperature >38.1°C, nausea 4
• White blood cell count >9000/μL 4

Common Documentation Pitfalls

Avoid these coding errors:

• Do not use confirmed COVID-19 codes (U07.1) without positive diagnostic testing 1
• Do not use "suspected" codes (U07.2) after negative testing; switch to symptom codes or Z03.818 1
• Do not code based on imaging alone; chest CT findings require correlation with clinical presentation and testing 6, 2
• Document timing of symptom onset relative to exposure, as this affects testing strategy and code selection 1

Special Populations

Asymptomatic Exposed Individuals

For asymptomatic individuals with known exposure who require testing for epidemiologic or clinical reasons (immunocompromised, high-risk contacts), use Z20.828 until test results return 1. If testing positive while asymptomatic, use U07.1 with documentation of asymptomatic status 1.

Coinfection Scenarios

COVID-19 and influenza coinfection occurs in approximately 0.54% of cases 7. When both are confirmed, code both conditions separately using U07.1 and the appropriate influenza code 7.