What are the criteria and pretesting assessment for the BTNX (Biotechnology Network Exchange) Covid (Coronavirus Disease 2019) and Influenza A/B Lateral Flow Assay?

BTNX COVID-19 & Influenza A/B Lateral Flow Assay: Criteria and Pretesting Assessment

The BTNX lateral flow assay should be used primarily for symptomatic patients within 5 days of symptom onset, with specimen collection via anterior nasal, midturbinate, or nasopharyngeal swabs, and negative results must be confirmed with NAAT when clinical suspicion remains moderate to high. 1

Patient Selection Criteria

Symptomatic Patients (Primary Indication)

• Test symptomatic individuals with at least one common symptom of COVID-19 or influenza within 5 days of symptom onset for optimal performance 1
• Common symptoms include fever, cough, sore throat, myalgia, headache, and respiratory distress 1
• The BTNX assay demonstrated specificity ranging from 96-100% in head-to-head evaluations, making positive results reliable for treatment decisions 2

Asymptomatic Patients with Known Exposure

• Consider testing asymptomatic individuals with documented exposure to SARS-CoV-2 or influenza within the preceding 14 days 1
• Recognize that sensitivity is significantly lower in asymptomatic individuals compared to symptomatic patients 1

Patients NOT Appropriate for This Test

• Do not use for asymptomatic screening prior to procedures or hospital admission unless part of outbreak investigation 1
• Avoid using to guide discontinuation of isolation in recovering COVID-19 patients 1
• Not recommended for surveillance testing in completely asymptomatic individuals without known exposure 1

Specimen Collection Requirements

Approved Specimen Types

• Anterior nasal swabs, midturbinate swabs, or nasopharyngeal swabs are acceptable 1
• Nasopharyngeal specimens may provide superior pathogen detection compared to throat swabs 3
• Proper technique requires swabbing the posterior pharynx and tonsillar surfaces bilaterally when collecting throat specimens 3

Collection Method

• Either self-collected or healthcare provider-collected specimens are acceptable for anterior nares and midturbinate samples 1
• Both observed and unobserved self-collection are acceptable 1
• Specimens should be collected as close to illness onset as possible 1

Timing Considerations

Optimal Testing Window

• Perform testing within 5 days of symptom onset to optimize sensitivity 1
• Most antigen tests have FDA indications for use within the first 5,7,12, or 14 days of symptom onset depending on the specific test 1
• Testing performed late in the course of infection has significantly reduced sensitivity 1

When to Repeat Testing

• If the first antigen test is negative and NAAT results are unavailable, repeat antigen testing within 5 days of symptom onset 1
• No need for repeat testing if the first antigen test is positive 1

Pretesting Clinical Assessment

Risk Stratification

• Perform point-of-care risk assessment including clinical presentation, epidemiological history, and travel history 1
• Screen all patients for fever (temperature >37.5°C) and upper respiratory symptoms before testing 1
• Assess for known exposure to confirmed COVID-19 or influenza cases within 14 days 1

Clinical Suspicion Level

• High clinical suspicion: Patients with typical symptoms, known exposure, or radiographic findings suggestive of viral pneumonia 1
• Moderate clinical suspicion: Patients with some compatible symptoms but no clear exposure history 1
• Low clinical suspicion: Patients with minimal or atypical symptoms and no known exposure 1

Interpretation and Confirmation Requirements

Positive Results

• A positive BTNX lateral flow assay has high specificity and can guide treatment and isolation decisions without confirmation 1
• Positive results are reliable for initiating antiviral therapy within the 5-day treatment window 1

Negative Results

• Negative antigen results MUST be confirmed with standard NAAT (rapid RT-PCR or laboratory-based NAAT) if clinical suspicion for COVID-19 or influenza remains moderate or high 1
• Antigen tests are less sensitive than NAAT, especially in asymptomatic individuals or late in infection 1
• If standard NAAT is unavailable or results will be delayed more than 1 day, the antigen test alone is acceptable 1

Special Population Considerations

Limited Data Populations

• Limited data exist regarding analytical performance in children, immunocompromised patients, and vaccinated individuals 1
• Exercise increased caution when interpreting results in these populations 1

Coinfection Considerations

• Be aware that COVID-19 and influenza coinfection occurs in approximately 0.5% of cases 4
• The BTNX combo assay can detect both pathogens simultaneously, which is valuable during overlapping respiratory virus seasons 2, 4

Common Pitfalls to Avoid

• Never assume a negative antigen test rules out infection in symptomatic patients with high clinical suspicion—always confirm with NAAT 1
• Do not test beyond 5 days of symptom onset without understanding the significantly reduced sensitivity 1
• Avoid using antigen testing as the sole basis for discontinuing isolation precautions 1
• Do not delay necessary treatment while awaiting confirmatory NAAT if clinical suspicion is high and the patient is within the antiviral treatment window 1
• Be aware that cross-reactivity with other seasonal coronaviruses (CoV-229E, CoV-NL63, CoV-OC43) has been observed in some lateral flow assays 2

Advantages of BTNX Lateral Flow Platform

• Results available within approximately 15 minutes, enabling same-encounter decision-making 1
• Generally less expensive than NAAT 1
• Can be performed at point-of-care or at home without specialized equipment 1
• Targets nucleocapsid proteins, which are less affected by viral mutations compared to spike protein targets 1