COVID-19 Investigations (Diagnostic, Monitoring & Severity Assessment Protocol)

Appropriate investigations in COVID-19 serve four major purposes:

1. Confirm the diagnosis of SARS-CoV-2 infection

2. Identify differential diagnoses and co-infections

3. Assess disease severity and complications

4. Monitor disease progression and response to treatment

I. Diagnostic Laboratory Investigations

1. Confirmatory Testing for SARS-CoV-2

Routine confirmation of COVID-19 is based on detection of viral RNA using:

• Real-time Reverse Transcriptase Polymerase Chain Reaction (rRT-PCR)

• Other validated Nucleic Acid Amplification Tests (NAATs)

These remain the diagnostic gold standard.

Antigen Testing

Rapid antigen tests may be used according to national guidelines, particularly where PCR is unavailable or when rapid diagnosis is required.

2. Specimen Collection

Specimen collection, transport, processing, and testing should strictly follow biosafety procedures.

Respiratory Specimens

Whenever feasible, collect specimens from both:

Upper Respiratory Tract (URT)

• Nasopharyngeal swab

• Oropharyngeal swab

Lower Respiratory Tract (LRT)

• Expectorated sputum

• Endotracheal aspirate

• Bronchoalveolar lavage (BAL)

LRT specimens generally contain higher viral loads and may improve diagnostic sensitivity.

Clinicians may collect only LRT specimens when these are readily available, such as in mechanically ventilated patients.

Personal Protective Equipment During Sampling

Appropriate PPE should always be used.

URT specimen collection

• Droplet precautions

• Contact precautions

LRT specimen collection

• Airborne precautions

• Contact precautions

Important Collection Notes

When collecting URT specimens:

• Use sterile Dacron or Rayon swabs

• Do not use cotton swabs

• Place specimens in Viral Transport Medium (VTM)

Avoid collecting specimens directly from the nostrils or tonsils, as these reduce diagnostic accuracy.

Blood Cultures

Blood cultures should be collected when bacterial pneumonia or sepsis is suspected.

Ideally:

• Obtain blood cultures before starting antibiotics

• Do NOT delay antimicrobial therapy while awaiting blood culture results.

II. Investigation of Differential Diagnoses and Co-Infections

COVID-19 frequently mimics numerous infectious diseases. Evaluation for alternative diagnoses and co-infections is essential.

Common Causes of Community-Acquired Pneumonia

Investigations should consider:

• Streptococcus pneumoniae

• Haemophilus influenzae type b

• Staphylococcus aureus

• Klebsiella pneumoniae

• Legionella pneumophila

• Influenza viruses

• Respiratory Syncytial Virus (RSV)

Other Respiratory Viral Testing

Where laboratory capacity allows, respiratory specimens should also be tested for:

• Influenza A

• Influenza B

• Zoonotic Influenza A

• Respiratory Syncytial Virus (RSV)

• Parainfluenza viruses

• Rhinoviruses

• Adenoviruses

• Enteroviruses (including EV-D68)

• Human metapneumovirus

• Endemic human coronaviruses:

  • HKU1

  • OC43

  • NL63

  • 229E

Other Differential Diagnoses

COVID-19 should be differentiated from:

Respiratory Diseases

• Influenza

• Bacterial pneumonia

• Pulmonary tuberculosis

Tropical Febrile Illnesses

• Malaria

• Dengue fever

• Typhoid fever

Cardiovascular Diseases

• Acute coronary syndrome

• Myocarditis

• Heart failure

Renal Disorders

• Acute kidney injury

• Uremia

Systemic Infection

• Non-respiratory sepsis

III. Imaging Investigations

Imaging helps determine pulmonary involvement, assess disease severity, and identify complications such as ARDS, pulmonary embolism, or cardiac strain.

1. Chest X-Ray (CXR)

First-line imaging modality

Indications

• Symptomatic patients

• Hospitalized patients

• Follow-up of disease progression

Typical Findings

Advantages

• Widely available

• Portable bedside imaging

• Useful for serial monitoring

2. Lung Ultrasound (LUS)

Useful in:

• ICU patients

• Low-resource settings

• Bedside assessment

Findings

• Multiple B-lines

• Pleural line irregularities

• Subpleural consolidations

• Pleural effusion (rare; suggests an alternative diagnosis)

3. High Resolution CT Chest (HRCT)

Reserved for referral centres or diagnostic uncertainty.

Typical Findings

• Bilateral ground-glass opacities

• Peripheral distribution

• Posterior predominance

• Crazy-paving pattern

• Consolidation in severe disease

Indications

• Severe respiratory symptoms

• Clinical deterioration

• Suspected pulmonary embolism

• Fibrosis assessment

• Discordant PCR and clinical findings

Repeat Imaging

• Baseline imaging at admission when indicated

• Repeat after approximately 7 days

• Earlier if clinical deterioration occurs

• Later if clinical improvement is observed

IV. Routine Baseline Laboratory Investigations

The following investigations should be performed on admission whenever available.

V. Additional Essential Investigations

Microbiology

• Blood culture (suspected sepsis)

• Sputum culture (productive cough)

• Stool culture (persistent diarrhea)

Physiological Assessment

• Arterial Blood Gas (ABG)

• ECG

• Cardiac enzymes (troponin) if chest pain or suspected myocarditis

VI. Mandatory Admission Investigations

VII. Prognostic Laboratory Markers

These investigations help predict deterioration and mortality.

High-Risk Laboratory Pattern

The following pattern suggests impending severe or critical disease:

• Progressive lymphopenia

• Rapidly rising CRP

• Rising ferritin

• Increasing D-dimer

• Elevated LDH

• Elevated troponin

• Worsening ABG parameters

VIII. Follow-Up (Monitoring) Investigations

Monitoring frequency depends on disease severity.

Daily Monitoring

• Oxygen saturation (SpO₂)

• Blood glucose

• Urine output

• Vital signs

Every 48 Hours (or as clinically indicated)

• CRP

• Ferritin

• D-dimer

• Procalcitonin

Twice Weekly

• CBC

• Electrolytes

• Renal function tests

• Liver function tests

Imaging Follow-Up

IX. COVID-19 Severity Classification

1. Asymptomatic or Pre-symptomatic Infection

• Positive NAAT or antigen test

• No symptoms consistent with COVID-19

2. Mild Illness

Symptoms may include:

• Fever

• Cough

• Sore throat

• Malaise

• Headache

• Myalgia

• Nausea

• Vomiting

• Diarrhea

• Loss of taste or smell

No:

• Shortness of breath

• Dyspnea

• Abnormal chest imaging

3. Moderate Illness

• Evidence of lower respiratory tract disease clinically or on imaging

• SpO₂ ≥94% on room air (at sea level)

4. Severe Illness

One or more of the following:

• SpO₂ <94% on room air (at sea level)

• PaO₂/FiO₂ <300 mmHg

• Respiratory rate >30 breaths/min

• Lung infiltrates involving >50% of the lung fields

5. Critical Illness

Presence of any of the following:

• Respiratory failure requiring advanced respiratory support

• Septic shock

• Multiple organ dysfunction or failure

X. Clinical Interpretation Principles

• Laboratory deterioration often precedes clinical deterioration.

• Rising D-dimer should prompt evaluation for venous thromboembolism.

• Rising CRP and ferritin suggest hyperinflammation or cytokine storm.

• Increasing procalcitonin indicates possible bacterial superinfection.

• Worsening ABG reflects progressive respiratory failure.

• Blood cultures should be obtained before antibiotics whenever feasible, but treatment should never be delayed while awaiting results.

Key Takeaway

COVID-19 investigations should be dynamic rather than static. A combination of microbiological testing, imaging, routine laboratory investigations, prognostic biomarkers, and repeated clinical assessment provides the most accurate evaluation of disease severity, guides treatment decisions, detects complications, and predicts clinical outcomes. Repeated measurements over time are generally more informative than a single baseline investigation.