What is the lung ultrasound score, how is it calculated across the twelve lung zones, and how do its values guide management decisions in patients with acute respiratory distress syndrome, pneumonia, or COVID‑19?

Lung Ultrasound Score: Definition, Calculation, and Clinical Application

What is the Lung Ultrasound Score?

The lung ultrasound score (LUS or LUSS) is a semi-quantitative bedside assessment tool that grades lung aeration loss across twelve thoracic zones, with each zone scored 0–3 based on ultrasound artifacts, yielding a total score of 0–36 that directly correlates with disease severity and predicts clinical outcomes in ARDS, pneumonia, and COVID-19. 1, 2

Calculation Methodology Across Twelve Zones

Zone Division and Scanning Technique

• Divide each hemithorax into six regions: anterior mid-clavicular (apical, medial, basal), lateral mid-axillary (apical, basal), and posterior para-spinal (apical, medial, basal), creating twelve total zones bilaterally. 3

• Use convex or linear transducers with single-focal point modality set at the pleural line; perform intercostal scanning (not orthogonal to ribs) to maximize pleural surface visualization. 3

Scoring System for Each Zone

• Score 0 (normal aeration): A-lines present with fewer than three B-lines, indicating normal lung aeration 1, 4

• Score 1 (moderate aeration loss): Three or more well-separated B-lines (vertical artifacts) indicating interstitial syndrome 1, 4

• Score 2 (severe aeration loss): Confluent B-lines creating a "white lung" appearance, equivalent to CT ground-glass opacities 3, 1

• Score 3 (complete aeration loss): Lung consolidation with tissue-like appearance (hepatization) with or without air bronchograms 3, 1

Total Score Interpretation

• Sum all twelve zone scores to obtain the total LUS score (range 0–36). 2, 4, 5

• Higher scores indicate greater loss of lung aeration and more severe disease. 2, 4

Clinical Decision-Making Based on LUS Score Values

COVID-19 Specific Thresholds

A LUS score ≥20 at hospital admission predicts significantly increased in-hospital mortality (hazard ratio 9.87) and should trigger immediate ICU-level monitoring. 3

• LUS score >12 predicts PaO₂/FiO₂ ratio <200 with 97.37% sensitivity and 85.7% specificity, indicating severe ARDS requiring mechanical ventilation. 4

• LUS score of 25 at ICU admission serves as a critical cut-off (OR 1.1) for mortality prediction in COVID-19 patients. 5

Management Algorithm by Score Range

LUS score 0–12 (mild disease):

• Outpatient management may be appropriate if clinically stable without risk factors 1
• Serial monitoring every 24–48 hours to detect progression 1

LUS score 13–19 (moderate disease):

• Hospital admission to regular ward indicated 1
• Supplemental oxygen as needed to maintain SpO₂ >93% 1
• Daily LUS reassessment to guide escalation decisions 3

LUS score 20–24 (severe disease):

• ICU admission strongly recommended 3, 5
• High-flow nasal oxygen or non-invasive ventilation 1
• Consider prone positioning 1

LUS score ≥25 (critical disease):

• Immediate ICU admission mandatory 5
• Prepare for mechanical ventilation 3
• Monitor for complications including pneumothorax, pleural effusion, and pulmonary embolism 3

Monitoring Disease Trajectory

Serial LUS scoring provides critical prognostic information: survivors demonstrate significantly lower score differences between admission and discharge (mean difference 1.75), while persistently high or increasing scores predict mortality. 5

• Improvement category (negative ΔLUS) correlates with increased normally aerated lung regions on CT and better outcomes. 6

• Worsening category (positive ΔLUS) correlates with increased non-aerated regions and higher mortality risk. 6

Comparative Performance and Clinical Context

Sensitivity Advantages Over Chest Radiography

• LUS demonstrates 80% sensitivity for pneumonia detection compared to chest X-ray's 43.5–69% sensitivity, making it superior for early disease detection. 3, 1, 7

• LUS detects pleural thickening, subpleural consolidation, and ground-glass equivalents with sensitivity comparable to CT (92–93%). 3

Correlation with CT and Clinical Parameters

LUS score shows strong negative correlation with PaO₂/FiO₂ ratio (ρ = -0.827) and lung compliance (ρ = -0.634), while positively correlating with lung resistance (ρ = 0.735). 4

• LUS score correlates strongly with CT severity score (Pearson r = 0.754, R² = 0.568) for quantifying COVID-19 lung involvement. 3

• Changes in LUS score (ΔLUS) correlate significantly with changes in CT-measured lung aeration (r = -0.74). 6

Specific Clinical Scenarios

ARDS Management

In mechanically ventilated ARDS patients, LUS score reliably monitors time-dependent changes in lung aeration across ventral, intermediate, and dorsal zones, guiding ventilator adjustments and prone positioning decisions. 6

Pneumonia Diagnosis

LUS serves as a first-line diagnostic tool when CT is unavailable, with 93–96% sensitivity and specificity for detecting pneumonia, particularly useful for identifying subpleural consolidations missed on chest X-ray. 3, 7

COVID-19 Triage and Escalation

LUS at emergency department presentation stratifies patients into risk categories: negative scan with clinical stability allows outpatient management, while scores >20 mandate hospitalization regardless of initial clinical appearance. 3, 1, 2

• LUS predicts need for ICU admission, intubation, and mortality more accurately than chest X-ray alone. 2

• When combined with National Early Warning Score (NEWS), LUS provides incremental predictive value for mortality within each NEWS stratum. 2

Critical Pitfalls to Avoid

Do not use LUS as the sole diagnostic tool for centrally located consolidations or bacterial superinfection, as these may be missed due to ultrasound's limited penetration depth. 3

Do not assume LUS can distinguish acute from chronic lung pathology in patients with pre-existing pulmonary conditions; clinical correlation and comparison with prior imaging are essential. 3

Do not perform LUS without proper infection control precautions: the operator must maintain 30–50 cm proximity for 10–60 minutes, requiring droplet/contact precautions and appropriate PPE including N95 masks for aerosol-generating procedures. 3

Do not delay CT imaging when pulmonary embolism is suspected, as LUS cannot reliably detect pulmonary arterial thrombosis despite its utility for parenchymal assessment. 3

Do not rely on a single LUS assessment; serial examinations every 24–48 hours are necessary to detect disease progression, particularly in the first week when COVID-19 pneumonia peaks at 10–12 days from symptom onset. 3