Necrotizing Soft Tissue Infection LRINEC Score

Evaluates whether diagnosis of necrotizing fasciitis is likely, based on 6 clinical determinations.

In the text below the calculator there is more information about the score, its interpretation and the study it is based on.

The LRINEC score helps clinicians diagnose necrotizing soft tissue infection (necrotizing fasciitis) based on clinical determinations like C reactive protein, WBC count, haemoglobin or serum sodium.

LRINEC comes from the Laboratory Risk Indicator for Necrotizing Fasciitis observational study that developed the score.

The score should be administered to patients where this type of infection is suspected, even when there is an assumed minor risk of nec. fasc. However, the score cannot rule out infection so most patients still have to undergo surgical consultation.

The table below summarizes the three categories of LRINEC scores and their associated risk of positive diagnosis:

LRINEC score	Positive diagnosis risk	Recommendation
0 - 5	Less than 50%	The patient should be monitored and administered IV antibiotics.
6, 7	Between 50 and 75%	Urgent MRI evaluation and frozen biopsy are required.
≥8	Risk of PPV of 92% and NPV of 96%	High likelihood for the patient to require operative debridement.

C Reactive Protein

Below 150 mg/L (0 points)

Equal to or above 150 mg/L (4 points)

White Blood Cell count

Below 15 per mm³ (0 points)

Between 15 and 25 per mm³ (1 point)

Above 25 per mm³ (2 points)

Hemoglobin

Above 13.50 g/dL (0 points)

Between 11 and 13.5 g/dL (1 point)

Below 11 g/dL (2 points)

Serum Sodium

Equal or higher than 135 mEq/L (0 points)

Below 135 mEq/L (2 points)

Creatinine

Below or equal to 1.6 mg/dL (141 mmol/L) (0 points)

Above 1.6 mg/dL (141 mmol/L) (2 points)

Glucose

Equal to or below 180 mg/dL (10 mmol/L) (0 points)

Above 180 mg/dL (10 mmol/L) (1 point)

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LRINEC explained

In 2004, the Laboratory Risk Indicator for Necrotizing Fasciitis observational study devised an evaluation score that can standardize pre-diagnostic assessment of patients suspected of necrotizing fasciitis and which can differentiate between this and other conditions (severe cellulitis or abscess).

The score should be administered to patients suspected of necrotizing fasciitis, even where there is assumed only a minor risk.

The clinical determinations used are common for diagnosis of most soft tissue conditions.

The LRINEC score consists of six items, each being a laboratory test result, each awarded a number of points, depending on its independent predictive value for positive diagnosis.

The table below describes the six items:

LRINEC item	Answer choices (points)	Description
C Reactive Protein	Below 150 mg/L (0) Equal to or above 150 mg/L (4)	Serologic measure of the acute phase reactant, liver protein released in the blood flow after tissue injury. CRP is a sign of infection and/or inflammation.
White Blood Cell count	Below 15 per mm³ (0) Between 15 and 25 per mm³ (1) Above 25 per mm³ (2)	Rises in WBC usually signal infection.
Hemoglobin	Above 13.50 g/dL (0) Between 11 and 13.5 g/dL (1) Below 11 g/dL (2)	Protein on erythrocytes, in charge with oxygen transport.
Serum Sodium	Equal or higher than 135 mEq/L (0) Below 135 mEq/L (2)	Evaluates electrolyte, acid-base and renal function.
Creatinine	Below or equal to 1.6 mg/dL (141 mmol/L) (0) Above 1.6 mg/dL (141 mmol/L) (2)	Measure of kidney filtration rate.
Glucose	Equal to or below 180 mg/dL (10 mmol/L) (0) Above 180 mg/dL (10 mmol/L) (1)	In diabetic patients strict glycemic control should be maintained and even supplemented with IV insulin if necessary.

The LRINEC score does benefit from the specificity to put a prospective diagnosis, early in the course of the disease, especially in patients with cellulitis signs.

The main limitation of the study is the fact that it doesn’t have enough relevant sensitivity as to rule out infection.

Therefore, in most cases, if the score strengthens the physician’s suspicion, the patient still requires a surgical consultation to check whether operative debridement is necessary.

Result interpretation

The LRINEC score is aimed at distinguishing between necrotizing fasciitis and other non-necrotizing soft tissue infections.

The total score ranges between 0 and 13 and has an established cut-off at 6 points. However, the patients are divided in three categories.

The table below summarizes the LRINEC scores, their associated risk of positive diagnosis and management recommendations:

LRINEC score	Positive diagnosis risk	Recommendation
0 - 5	Less than 50%	The patient should be monitored and administered IV antibiotics.
6, 7	Between 50 and 75%	Urgent MRI evaluation and frozen biopsy are required.*
≥8	Risk of PPV of 92% and NPV of 96%	High likelihood for the patient to require operative debridement.

*If these are positive, then operative debridement is necessary. If negative, the patient should still receive IV antibiotics and be monitored.

About the study

The score is based on a 2004 study by Wong et al. that aimed to standardize the early recognition of NF, a condition which is complex to diagnose, especially from other soft tissue infections.

The study involved two cohorts of patients: a developmental one of 314 patients and a validation one of 140 patients.

From these patients, 145 were diagnosed with necrotizing fasciitis and 309 patients with severe cellulitis or abscesses. In the developmental cohort there were 89 patients with NF.

Hematologic and biochemical results done on admission were converted into categorical variables for analysis and univariate and multivariate logistic regression was used to extract significant predictors.

A cutoff value at 6 points with a positive predictive value of 92.0% and negative predictive value of 96.0%, was established. Whilst the cut-off can be reasonably used to establish diagnosis, it cannot be used to rule out NF as in the study, 10% of subjects diagnosed with NF still had a score of 6 points.

The score performance was deemed very good, with the area under the receiver operating characteristic curve being 0.980 in the developmental cohort and 0.976 in the validation cohort.

The score was deemed to be efficient in detecting clinically early cases of necrotizing fasciitis.

Necrotizing fasciitis guidelines

NF is one of the rapidly progressive infections of the fascia and subcutaneous tissue. Early recognition is essential in ensuring risk free prognosis and in avoiding complications. Left undiagnosed and untreated, the condition can lead to limb amputation or be life threatening.

There are bacterial causes to NF, such as the Group A streptococcus (Streptococcus pyogenes), Staphylococcus aureus or the Clostridium perfringens.

Other risk factors include obesity, substance abuse, surgery or trauma but also conditions in which there is immunosupresion, diabetes mellitus or chronic systemic disease.

Operative findings of necrotizing fasciitis include:

■ Grayish necrotic fascia;

■ Lack of bleeding of the fascia during dissection;

■ Lack of resistance of normally adherent muscular fascia to blunt dissection;

■ Foul-smelling “dishwater”.

Treatment comprises of sudden operative debridement, fluid resuscitation and administration of IV antibiotic. Preferred abx therapy is with vancomycin and clindamycin. In some case, post surgical debridement and skin grafting may become necessary.