APRI Calculator

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 - a value used to make the calculations more specific. Most experts recommend using the value of 40, expressed in IU/L; and

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

We can interpret the 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); and

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

The percentages above are the 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).

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

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

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

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

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

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

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

The third value, AST upper limit, is optional. It is, by default, 40 IU/L, but you can change if you need.

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

• AST level - 110 IU/L;
• AST upper limit - 40 IU/L; and
• 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 likely has severe fibrosis or cirrhosis.