Fibrotic NASH Index (FNI) Calculator

Overview

Who should take the test?

Individuals with 1 or more of the following conditions:

• Overweight (BMI ≥25 kg/m²)
• Obesity (BMI ≥30 kg/m²)
• Type 2 diabetes
• Metabolic syndrome:

International Diabetes Federation (IDF) definition (2005)
Central obesity	Waist circumference ≥ 94/80 cm in men/women (European ancestry) or BMI > 30 kg/m²
Plus any two of the following:
Triglycerides	≥ 1.7 mmol/L (150 mg/dL) or specific treatment for this lipid abnormality
HDL cholesterol	< 1.03 mmol/L (40 mg/dL) in men < 1.29 mmol/L (50 mg/dL) in women or specific treatment for this lipid abnormality
Blood pressure	Systolic ≥ 130 mmHg or diastolic ≥ 85 mmHg or treatment of previously diagnosed hypertension
Fasting plasma glucose	≥ 5.6 mmol/L (100 mg/dL) or previously diagnosed type 2 diabetes

Outcome

• Fibrotic NASH: histological diagnosis of NASH + elevated NAS score (NAS≥4) + significant fibrosis (F≥2)

Formula

$$FNI = \dfrac{e^{\left(\alpha + \beta + \gamma + \delta \right)}}{ 1+e^{\left(\alpha + \beta + \gamma + \delta \right)}};$$
where:
$$\alpha = -10.33;$$
$$\beta = +2.54 \times \ln \left(AST \left[ U/L\right] \right);$$
$$\gamma = +3.86 \times \ln \left(HbA1c \left[ \%\right] \right);$$
$$\delta = -1.66 \times \ln \left(HDL \left[ mg/dL \right] \right);$$

The score was developed in the derivation cohort (264 morbidly obese individuals) using a bootstrapping stepwise logistic regression model (2000 bootstrap samples). The score was derived based on the final predictors and the corresponding regression coefficients. Performance for fibrotic NASH was assessed by the receiver operating characteristic curve (AUROC). Rule-out and rule-in cut-offs were derived based on sensitivity ≥0.89 and specificity ≥0.90, respectively.

Interpretation

The FNI is a predicted probability score derived from a logistic regression model, and it ranges from 0 to 1.

Performance and cut-offs