AST to Platelet Ratio Index (APRI)
WARNING: Do NOT use APRI alone as its accuracy rate is not sufficient to do so; experts recommend using a combination of two or all three of the non-invasive liver tests (APRI, FibroSure/FibroTest, or FibroScan).
Using the results of APRI, a non-invasive test, one can very roughly determine whether one has a high risk of having advanced liver damage. It is not particularly useful in telling the exact Metavir stage; it simply provides ‘one piece of the puzzle’. To compute APRI one only needs to know the most current AST score and PLATELET Count, both of which are on most blood panels regularly given to HCV+ patients.
SOURCE: “A Simple Noninvasive Index Can Predict Both Significant Fibrosis and Cirrhosis in Patients with Chronic Hepatitis C” by Chu-Tao Wai, Joel K. Greeson, et al, HEPATOLOGY Vol. 38, #2, 2003, pp 518-526.
- Divide the AST by 35*.
- Divide that number by the PLATELET count (this should be in the range 0 to 500 or so – if there are extra zeros, delete these before computing).
- Multiply this number by 100.
- If this number is greater than 0.5, there is a good chance they have some liver damage. If greater than 1.5, the person very likely has cirrhosis. One can say APRI scores between 0.5 to 1.5 VERY LOOSELY correspond to Metavir Stages 1-3, and above 1.5 corresponds (again, very loosely) to Metavir Stage 4.
*Why divide by 35??
You are supposed to divide the AST by the “Upper Limit of Normal” (ULN) AST. This number is sometimes disputed, and varies from lab to lab. Most seem to be in the range of 35-45. Gender is another factor: women’s normal scores tend to be somewhat lower than men, so their “Upper Limit of Normal” should be considered slightly lower than men’s as well. If this lower ULN is not used in computing APRI, a woman’s liver disease may be further advanced when it is first detected.
Sample APRI Computations of three HCV+ individuals:
From a recent blood test, Donald got these scores
— AST= 232
— Blood Platelet count= 94
Donald’s APRI =(232/35)/94*100=7.05
Conclusion: Donald likely has advanced liver damage, and is probably cirrhotic.
From a recent blood test, Linda got these scores
–Blood Platelet count=150
Conclusion: Linda probably has some liver damage, but it is likely not very advanced yet.
–Blood Platelet count=250
Conclusion: Robert probably does not have any serious liver damage yet.