LRINEC Score Calculator (laboratory risk of necrotising fasciitis)

Understanding the LRINEC score calculator — concept and principle

The LRINEC score (Laboratory Risk Indicator for Necrotising Fasciitis) adds points for six routine blood tests to estimate how likely a severe soft-tissue infection is to be necrotising fasciitis, a fast-spreading, life-threatening infection. Emergency and surgical teams use it as one piece of evidence when the diagnosis is uncertain.

How it is calculated

LRINEC (0–13) = sum of:

• CRP 150 mg/L or more → 4
• White cells 15–25 ×10³/µL → 1; above 25 → 2
• Haemoglobin 11–13.5 g/dL → 1; below 11 → 2
• Sodium below 135 mmol/L → 2
• Creatinine above 141 µmol/L (1.6 mg/dL) → 2
• Glucose above 180 mg/dL (10 mmol/L) → 1

Risk groups: 5 or less low, 6–7 intermediate, 8 or more high.

The principle

Wong and colleagues (2004) compared blood tests in patients with necrotising fasciitis and other severe soft-tissue infections and weighted the tests that differed most. Very high CRP reflects intense inflammation; a high white count, low sodium, kidney impairment and high glucose reflect systemic illness; and falling haemoglobin can follow tissue destruction and haemolysis.

Worked example

Default inputs: CRP 180 mg/L, white cells 18, haemoglobin 12.5 g/dL, sodium 133, creatinine 1.4 mg/dL, glucose 150 mg/dL.

1. CRP 180 ≥ 150 → 4.
2. White cells 18 in 15–25 → 1.
3. Haemoglobin 12.5 in 11–13.5 → 1.
4. Sodium 133 < 135 → 2.
5. Creatinine 1.4 × 88.4 = 124 µmol/L, not above 141 → 0; glucose 150 → 0.
6. Total 8 → High (8 or more).

How to read the result

A high score supports urgent surgical assessment. However, the score was built retrospectively and later studies found that a low score does not rule the disease out: about one in ten patients with a score below 6 still had it. Severe pain out of proportion, rapid spread, skin changes and systemic toxicity should prompt urgent surgery regardless.

Common mistakes

• Using a low score to delay surgical review.
• Entering creatinine in µmol/L while the unit is set to mg/dL.
• Applying it to mild cellulitis, for which it was not designed.

Frequently asked questions

What LRINEC score suggests necrotising fasciitis?

6 or more raises suspicion and 8 or more is high risk, but clinical signs take priority.

How is necrotising fasciitis diagnosed?

Mainly by surgical exploration, supported by clinical findings and imaging.

Why does sodium matter?

Low sodium was more common in necrotising fasciitis in the derivation data, likely reflecting severe systemic illness.

Sources: Wong CH, Khin LW, Heng KS, Tan KC, Low CO, "The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections", Crit Care Med 2004;32(7):1535–1541