What is required for a clinical diagnosis of COVID-19 (Coronavirus Disease 2019)?

Clinical Diagnosis of COVID-19

RT-PCR testing is the gold standard and definitive diagnostic test for COVID-19 infection and should be performed as the first-line diagnostic test for all patients suspected of having the disease. 1

Diagnostic Testing Hierarchy

Primary Diagnostic Method

• RT-PCR test: The reference standard for confirming COVID-19 diagnosis 2, 1
  • Specimen collection (in order of preference):
    • Nasopharyngeal (NP) swab
    • Midturbinate (MT) swab
    • Combined anterior nasal (AN) plus oropharyngeal (OP) swab
    • Saliva or mouth gargle specimens 1

Secondary Diagnostic Methods

• Antigen tests: Lower sensitivity than RT-PCR but high specificity when positive 1
• Radiological assessment:
  • Chest CT scan: Most accurate radiological tool 1
  • Chest X-ray or lung ultrasound: When CT is unavailable 1

Clinical Criteria for Suspected COVID-19

When RT-PCR testing is unavailable or pending, clinical diagnosis should be based on:

1. Clinical symptoms 2, 1:

   • Fever
   • Cough
   • Shortness of breath
   • Anosmia/hyposmia (has high positive likelihood ratio of 7.58) 3
   • Dysgeusia
   • Gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea)

2. Laboratory findings 1:

   • Lymphopenia
   • Elevated inflammatory markers (CRP, ferritin, IL-6, ESR, procalcitonin)
   • Elevated D-dimer
   • Thrombocytopenia

3. Radiological findings 1:

   • Bilateral B lines on lung ultrasonography (high positive likelihood ratio of 7.09) 3
   • Ground-glass opacities on chest CT
   • Bilateral infiltrates on chest X-ray

Important Diagnostic Considerations

1. False negatives with RT-PCR can occur, especially early in infection:

   • 100% false-negative rate on day 1 of infection
   • 68% false-negative rate on day 4
   • 20% false-negative rate 3 days after symptom onset 1

2. A negative chest CT scan does not exclude COVID-19, especially in early or asymptomatic cases 2, 1

3. When RT-PCR is unavailable, the patient should be managed as COVID-19 positive with all necessary precautions 2

4. Emergency physician clinical judgment has significant value:

   • High clinical probability assessment by emergency physicians correlates strongly with positive RT-PCR results 3
   • Low clinical probability assessment correlates with negative results 3

Management Algorithm When RT-PCR Testing is Unavailable

1. Assess clinical symptoms, laboratory markers, and radiological findings
2. If clinical suspicion is high based on symptoms and findings, manage as COVID-19 positive 2
3. Implement all protective measures and isolation protocols 2
4. For stable patients where COVID-19 cannot be ruled out, consider transfer to a COVID-19 hub hospital if available 2

Common Pitfalls to Avoid

1. Relying solely on radiological findings: A normal chest CT scan cannot exclude COVID-19 diagnosis, especially in early disease 2, 1

2. Waiting for RT-PCR results before isolation: Patients with suspected COVID-19 should be isolated immediately while awaiting test results 2

3. Using serum biomarkers alone to determine antibiotic therapy: Antibiotics should not be routinely prescribed for COVID-19 patients based solely on biomarkers 2, 1

4. Assuming RT-PCR is 100% sensitive: Consider repeat testing if clinical suspicion remains high despite initial negative results 1

By following this diagnostic approach, clinicians can effectively identify COVID-19 cases, implement appropriate isolation measures, and initiate timely treatment to improve patient outcomes.