How do I assess the severity of COVID‑19 infection in a patient?

Assessing COVID-19 Severity

COVID-19 severity should be classified into three categories: mild (no hypoxemia or significant dyspnea), moderate-to-severe (hypoxemia with oxygen saturation ≤93% at rest or moderate-to-severe dyspnea), and critical (respiratory failure requiring mechanical ventilation, septic shock, or multiorgan failure). 1

Clinical Severity Classification

Mild Disease

• No evidence of significant pulmonary dysfunction: absence of hypoxemia, no or mild dyspnea 1
• Patients can maintain oxygen saturation >93% on room air 1
• Minimal respiratory symptoms without respiratory distress 1

Moderate-to-Severe Disease

• Presence of hypoxemia: oxygen saturation ≤93% at rest 1
• Tachypnea: respiratory rate indicating respiratory distress 1
• PaO2/FiO2 ratio <300 mm Hg 1
• Moderate-to-severe dyspnea requiring oxygen supplementation 1

Critical Disease

• Respiratory failure requiring mechanical ventilation 1
• Septic shock 1
• Multiorgan dysfunction or failure requiring intensive care 1

Key Clinical Assessment Parameters

Vital Signs and Oxygen Status

• Oxygen saturation at rest is the single most important vital sign for severity assessment 1
• Respiratory rate and presence of tachypnea 1
• Heart rate elevation (associated with ICU admission) 2, 3
• Body temperature (fever correlates with progression) 3

Important caveat: Elderly patients may develop hypoxemia without respiratory distress, making oxygen saturation monitoring critical even in the absence of dyspnea 1

Symptom Assessment

• Respiratory symptoms: dyspnea, chest pain, shortness of breath are associated with severe disease 2, 4
• Gastrointestinal symptoms: nausea, vomiting, abdominal pain correlate with severe COVID-19 4
• Change in consciousness is a critical indicator of severe disease 3
• Fatigue is associated with increased severity 2

Laboratory Markers for Severity

Hematologic markers:

• Lymphocyte count: lymphocytopenia is strongly associated with severity and mortality 2, 3, 5
• Platelet count: abnormal platelets predict severe disease 3
• White blood cell count abnormalities 3

Inflammatory markers:

• C-reactive protein (CRP): elevated levels indicate severe disease 6, 2
• D-dimer elevation correlates with mortality 1, 2
• ESR elevation 6

Cardiac markers:

• Cardiac troponin I (cTnI) elevation indicates myocardial injury and severe disease 2
• B-type natriuretic peptide (BNP) elevation 2

Liver function tests:

• AST >273 U/L or ALT >108 U/L indicates severe liver injury requiring close monitoring 6
• AST:ALT ratio of 3:1 suggests severe hepatocellular injury 6, 7
• Elevated bilirubin (>1.2 mg/dL) occurs in 9-35% of cases 1, 6

Risk Factors for Disease Progression

Age and demographics:

• Age >60-65 years is the strongest demographic predictor 1, 2, 3, 4, 5
• Male sex increases risk of severe disease and mortality 2, 4

Comorbidities predicting severity:

• Diabetes mellitus (coefficient 23.4 for severity, 8.2 for mortality) 4
• Immunosuppression (coefficient 53.9 for severity) 4
• Malignancy (coefficient 23.4 for severity) 4
• Hypertension (coefficient 6.99 for mortality) 1, 4
• Cardiovascular disease 1
• Chronic respiratory disease 1
• Chronic kidney disease 3
• Dementia predicts both severe disease and progression 3

Imaging Assessment

Chest imaging indications for severity assessment:

• Imaging is advised for patients with risk factors for disease progression (age >65, comorbidities) who have mild features and positive COVID-19 testing or moderate-to-high pretest probability 1
• Imaging is advised for all patients with clinical worsening regardless of initial severity 1
• Bilateral opacities on chest radiograph or CT are common in severe disease 1
• Ground glass opacities and consolidation on CT are typical findings 1
• Lobular involvement score on CT predicts severity 2

Chest imaging should be used in addition to clinical and laboratory assessment to decide between regular ward admission versus ICU admission 1

Practical Severity Assessment Algorithm

1. Measure oxygen saturation at rest: <93% indicates moderate-to-severe disease 1
2. Assess respiratory symptoms: presence of dyspnea, tachypnea, or chest pain suggests progression 1, 4
3. Check for altered consciousness: indicates critical disease 3
4. Obtain laboratory tests: lymphocyte count, platelet count, CRP, D-dimer, cardiac markers (troponin, BNP), liver enzymes 6, 2, 3
5. Identify high-risk features: age >60-65, diabetes, immunosuppression, malignancy, cardiovascular disease 1, 4, 5
6. Consider chest imaging for patients with risk factors or clinical worsening 1

Common pitfall: Do not rely solely on respiratory symptoms in elderly patients, as they may develop severe hypoxemia without dyspnea 1. Always measure oxygen saturation objectively.

Prediction model: A logistic model adjusted by age, lobular involvement score on CT, and lymphocyte cell count can assess severity with 90.9% sensitivity and 78.1% specificity 2