LRINEC Score for Necrotizing Soft Tissue Infections
The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score should be used as a "rule-in" tool with a threshold of ≥6 points to support clinical suspicion and trigger immediate surgical consultation, but it must never be used to exclude necrotizing soft tissue infection (NSTI) due to poor sensitivity. 1
Score Calculation
The LRINEC score uses six routine laboratory parameters obtained at initial presentation, with a maximum total of 13 points: 2
- C-reactive protein >150 mg/L: 4 points
- White blood cell count >15,000/μL: 2 points
- Hemoglobin <13.5 g/dL: 2 points
- Sodium <135 mmol/L: 2 points
- Creatinine >1.6 mg/dL: 2 points
- Glucose >180 mg/dL: 1 point
Score Thresholds and Performance
LRINEC ≥6 points yields a sensitivity of 68.2% and specificity of 84.8%, with a positive predictive value of 57-64%. 1 This threshold should prompt urgent surgical consultation. 2
LRINEC ≥8 points increases specificity to 94.9% but drops sensitivity to only 40.8%, representing a 75% probability of NSTI in the original validation cohort. 1
Critical Limitations
The LRINEC score has inadequate sensitivity (43-68%) and will miss many true cases of NSTI. 1, 2, 3 A meta-analysis of 23 studies (n=5,982) confirmed that due to poor sensitivity, LRINEC should not be used to rule out NSTIs. 1
Clinical Application Algorithm
When LRINEC ≥6 with clinical suspicion:
- Obtain immediate surgical consultation without awaiting imaging results 2
- Clinical features warranting concern include pain out of proportion to findings, rapid progression, systemic toxicity, edema extending beyond erythema, or "wooden" feel to subcutaneous tissue 1, 4
When LRINEC <6 but high clinical suspicion persists:
- Proceed directly to surgical consultation regardless of the score 2, 5
- Time to operative debridement is the most critical determinant of outcome; delays for laboratory confirmation adversely affect survival 2, 5
Special populations requiring extra caution:
- Immunocompromised patients (diabetes, chronic kidney disease, immunosuppressive therapy) may exhibit normal or minimally elevated laboratory values despite severe necrotizing infection 2, 5
- These patients require a lower threshold for surgical exploration even with LRINEC <6 2
Key Clinical Pitfalls to Avoid
Never delay surgical consultation to calculate or wait for LRINEC results when clinical suspicion is high. 2, 4 The diagnosis of NSTI is primarily clinical, and imaging studies should not delay surgical intervention. 1
Do not rely on the absence of fever, hypotension, or crepitus to exclude NSTI. 3 Fever has only 46% sensitivity, hypotension 21% sensitivity, and crepitus appears in only a minority of early cases. 4, 3
Clinical judgment supersedes the LRINEC score in all circumstances. 2 When necrotizing fasciitis is suspected based on severe pain disproportionate to findings, systemic toxicity, or failure to respond to antibiotics within 24-48 hours, proceed to surgical exploration regardless of laboratory values. 1, 4
Comparison with Alternative Scores
The NECROSIS score (incorporating systolic blood pressure ≤120 mmHg, violaceous skin, and WBC ≥15×10³/μL) demonstrated a c-statistic of 0.75 in a prospective multicenter trial, though it requires further validation. 6 The NSTI assessment score (NAS) incorporating vital signs showed comparable accuracy to LRINEC (AUC 0.926 vs 0.903) but also requires external validation. 7
Despite these alternatives, the LRINEC score remains the most widely validated tool, but its primary utility is to confirm suspicion (rule-in) rather than exclude disease (rule-out). 1