What is the a-drop score?

The A-DROP Score

The A-DROP score is a Japanese clinical severity assessment tool for community-acquired pneumonia (CAP) that evaluates five parameters: Age (male ≥70 years, female ≥75 years), Dehydration (BUN ≥210 mg/L), Respiratory failure (SaO₂ ≤90% or PaO₂ ≤60 mmHg), Orientation disturbance (confusion), and low blood Pressure (systolic BP ≤90 mmHg), with scores ranging from 0-5 points. 1

Scoring Components

Each of the following parameters receives 1 point when present: 1

• Age criteria: Male ≥70 years OR female ≥75 years
• Dehydration: Blood urea nitrogen (BUN) ≥210 mg/L (≥21 mg/dL)
• Respiratory failure: Oxygen saturation (SaO₂) ≤90% OR partial pressure of oxygen (PaO₂) ≤60 mmHg
• Orientation disturbance: Presence of confusion
• Pressure: Systolic blood pressure ≤90 mmHg

Clinical Performance

The A-DROP score demonstrates excellent predictive accuracy for mortality in CAP patients, with an area under the receiver operating characteristic curve of 0.846 (95% CI: 0.790-0.903), which is equivalent to the CURB-65 scoring system. 1

The score performs comparably to other established severity assessment tools: 2

• A-DROP: AUC 0.88 (95% CI: 0.82-0.94)
• CURB-65: AUC 0.88 (95% CI: 0.82-0.94)
• Pneumonia Severity Index (PSI): AUC 0.89 (95% CI: 0.85-0.94)

Prognostic Significance

Procalcitonin levels correlate strongly with A-DROP scores (ρ = 0.61, P < 0.0001), and the combination of semi-quantitative procalcitonin testing with A-DROP scoring enhances mortality prediction in hospitalized CAP patients. 2

Thirty-day mortality increases progressively with higher A-DROP scores, and patients who are procalcitonin-positive (≥0.5 ng/mL) have significantly higher mortality rates than procalcitonin-negative patients (log-rank test, P < 0.001). 2

Relationship to CURB-65

A-DROP is a modified version of the British Thoracic Society's CURB-65 score, adapted for the Japanese population with different age cutoffs and substituting respiratory rate for oxygen saturation/PaO₂ measurements. 1

The key differences are:

• A-DROP uses gender-specific age thresholds (male ≥70, female ≥75) versus CURB-65's uniform age ≥65 years 1
• A-DROP assesses oxygen saturation/PaO₂ rather than respiratory rate ≥30/min 1
• A-DROP uses BUN ≥210 mg/L versus CURB-65's BUN >200 mg/L (7 mmol/L) 1

Clinical Application

The Japanese Respiratory Society recommends using A-DROP as part of their 6-point scale (0-5) to assess CAP severity and guide management decisions for hospitalized patients. 1, 2

Higher scores indicate greater disease severity and increased mortality risk, allowing clinicians to stratify patients for appropriate level of care and treatment intensity. 2