The aspartate aminotransferase to platelet ratio index, or APRI, is a way to measure fibrosis of the liver for those with hepatitis C. This scoring model is noninvasive, practical, and easy to use.
Over time, people who are living with hepatitis C can develop chronic liver inflammation and liver disease. As the liver becomes damaged, scarring — referred to as fibrosis — can occur. If too much fibrosis occurs in the liver, it can lead to cirrhosis, which is a life-threatening condition that causes the liver to shut down.
APRI is one of many different kinds of tests that are used to measure the levels of fibrosis and, in turn, cirrhosis of the liver. Other kinds of tests include:
- liver biopsies
- noninvasive serum markers
- radiological imaging
This test was developed in 2003 as a noninvasive alternative to liver biopsies. A biopsy is an invasive procedure that involves surgically taking a small piece of liver tissue to be examined under a microscope for signs of damage or disease.
To determine the APRI score, you need two things:
- a blood test to measure your aspartate aminotransferase (AST)
- a platelet count
AST — also called serum glutamic-oxaloacetic transaminase (SGOT) — is an enzyme that your liver produces. A high AST usually implies there is some kind of damage going on in the liver.
The AST enzyme is measured using a graph called a hepatogram. It’s measured in IU/L, or international units per liter. The platelet count is measured in platelets/cubic millimeter. The upper limit of the normal range (ULN) of the AST, is usually set to 40 or 42 IU/L.
Once you have all these pieces, they are plugged into a formula to determine your APRI score: [(AST/ULN AST) x 100]/Platelet count
The formula divides your AST by the Upper Limit of the Normal Range (40 or 42). Then it multiplies that result by 100. It then divides the answer by the platelet count.
The APRI Score has two cutoffs:
- lower cutoff: 0.5
- upper cutoff: 1.5
Generally speaking, if your APRI score is less than or equal to 0.5, it’s a strong indicator that there is very little to no fibrosis present. On the other hand, if your APRI score is 1.5 or higher, it’s a strong indicator of cirrhosis.
APRI scores that fall between the lower and upper cutoffs are organized into certain stages of fibrosis, such as Metavir F0 (no fibrosis) up to Metavir F4 (cirrhosis).
It’s important to remember, however, that not all blood tests accurately reflect the state of the liver. Sometimes the AST reading can fluctuate wildly. Still, because this test is so inexpensive and easy, it’s the preferred way to get an indicator of fibrosis progression in hepatitis C patients over time.
The APRI score cannot be used to predict liver fibrosis, but it’s a good way to screen and evaluate current levels of liver fibrosis in those living with hepatitis C.
When used in conjunction with other fibrosis tests, doctors can get an accurate reading of fibrosis levels. If there are conflicting results, a liver biopsy is usually inevitable. Liver biopsies still remain the best way to measure liver fibrosis for chronic HCV, but are invasive, costly, and run the occasional risk of complications. Since APRI is noninvasive, simple, inexpensive, and relatively accurate, it’s an excellent alternative.