APRI Calculator

Created by Joanna Michałowska, PhD candidate
Reviewed by Dominik Czernia, PhD candidate and Jack Bowater
Last updated: Feb 15, 2022

The APRI calculator computes the AST to Platelet Ratio Index (APRI), which we use to predict fibrosis and cirrhosis. Calculating a patient's APRI score allows clinicians to easily predict hepatic fibrosis without performing a more invasive medical tests, e.g., biopsy.

Are you interested in other calculators that can help assess whether or not a patient has liver disease? Check out the MELD calculator (Model for End-Stage Liver Disease) and the Child Pugh calculator.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment.

AST to Platelet Ratio Index - How to calculate APRI score?

The aspartate aminotransferase (AST) to platelet ratio index is an easy, non-invasive alternative to liver biopsy for identifying hepatic fibrosis. Currently, a biopsy is the most common method for diagnosing liver fibrosis. However, this procedure is associated with patient discomfort and, in some cases, complications.

Therefore, researchers developed APRI, an indirect biochemical marker of hepatic fibrosis. We calculate it using routine laboratory parameters, which reflect alterations in hepatic function. It was initially validated in patients with chronic hepatitis C (CHC), but can also be used to identify other common fibrotic liver diseases.

The formula used to calculate APRI is:

APRI = [(AST level / AST upper limit) / Platelet count] * 100

where,

AST level - the aspartate aminotransferase level of the patient, expressed in IU/L (international units per litre);

AST upper limit - most experts recommend using the value of 40, expressed in IU/L; and

Platelet count - the patient's platelet count, expressed in 10⁹/L.

APRI score - interpretation

We can interpret APRI score as follows:

  • Significant fibrosis: APRI threshold of 0.7 (77% sensitive and 72% specific);

  • Severe fibrosis: APRI threshold of 1.0 (61% sensitive and 64% specific);

  • Cirrhosis: APRI threshold of 1.0 (76% sensitive and 72% specific).

Where the percentages describe correlation coefficients:

*Sensitivity - ability to correctly identify those with the disease (true positive rate).

*Specificity - ability to correctly identify those without the disease (true negative rate).

Results based on the Performance of the Aspartate Aminotransferase-To-Platelet Ratio Index for the Staging of Hepatitis C-related Fibrosis: An Updated Meta-Analysis study.

Interpretation based on another systematic review Blood Tests to Diagnose Fibrosis or Cirrhosis in Patients With Chronic Hepatitis C Virus Infection:

  • lower APRI score (less than 0.5) is associated with a greater negative predictive value (and ability to rule out cirrhosis)

  • higher APRI score (greater than 1.5) is associated with a greater positive predictive value (and ability to rule in cirrhosis).

The APRI calculator

To find out the patient's APRI score, you need to enter only two values:

  1. AST level - aspartate aminotransferase level of the patient (expressed in IU/L, i.e., international units per litre)

  2. Platelet count - patient's platelet count (expressed in 10⁹/L)

The third value, AST upper limit, is optional. We set as default at 40 IU/L but you can change if you need.

Calculating APRI score - a practical example

Let's calculate APRI score for a patient with the following laboratory tests:

  • AST level - 110 IU/L
  • AST upper limit - 40 IU/L
  • platelet count - 110 * 10⁹/L.

APRI = [(AST level / AST upper limit) / Platelet count] * 100

APRI = [(110 / 40) / 110] * 100

APRI = [2.75 / 110] * 100

APRI = 0.025 * 100

APRI = 2.5

This patient is likely to have severe fibrosis or cirrhosis.

Joanna Michałowska, PhD candidate
AST level
IU/L
AST upper limit
IU/L
Platelet count
⋅10⁹/L
AST to Platelet Ratio Index
APRI score
APRI score interpretation:

▪️ Significant fibrosis: APRI threshold of 0.7 (77% sensitive and 72% specific);

▪️ Severe fibrosis: APRI threshold of 1.0 (61% sensitive and 64% specific); and

▪️ Cirrhosis: APRI threshold of 1.0 (76% sensitive and 72% specific).

There are no universal cut-off values for the APRI score, as it is not sufficiently sensitive to rule out significant diseases (especially with midrange values). The lower the APRI score (<0.5), the greater the negative predictive value, and ability to rule out cirrhosis. The higher the value (>1.5) the greater the positive predictive value and ability to rule in cirrhosis.

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