π©Έ APRI Calculator
A simple blood-test estimate of liver fibrosis.
AST to platelet ratio index
For informational purposes only, not medical advice. Consult a healthcare professional.
Liver biopsy is the gold standard for staging fibrosis, but it is invasive, expensive, and samples only a speck of the organ. The AST-to-platelet ratio index (APRI) offers a free alternative from two routine blood tests: as fibrosis advances, AST rises from liver injury while platelets fall from portal hypertension trapping them in the spleen.
This calculator applies the standard formula and the World Health Organization cutoffs used for hepatitis B and C staging. It is a screening aid that helps decide who needs elastography or biopsy, not a replacement for them.
How to use this calculator
Take AST and platelets from a recent blood panel, plus your lab's AST upper limit of normal.
Enter AST in IU/L.
Enter your lab's AST upper limit of normal (often 40 IU/L).
Enter the platelet count in x10^9/L, and read the APRI and its band.
The formula and cutoffs
APRI normalizes AST against the lab's own reference range, then divides by platelets and scales by 100.
The cutoffs come from studies in chronic hepatitis C and were adopted by WHO for hepatitis B as well. Sensitivity and specificity are good at the extremes and poor in the middle, which is why the indeterminate zone exists.
Worked example
AST 80 IU/L, lab ULN 40, platelets 120 x10^9/L. APRI = (80/40) / 120 x 100 = 2/120 x 100 = 1.67. That falls in the significant-fibrosis-likely band, above 1.5 but below the 2.0 cirrhosis cutoff: this patient needs elastography to stage properly.
Contrast AST 30, ULN 40, platelets 220: APRI = (30/40)/220 x 100 = 0.75/220 x 100 = 0.34, below 0.5. Significant fibrosis is unlikely, and routine monitoring is reasonable.
What your result means
Below 0.5: rules out significant fibrosis reasonably well; keep managing the underlying liver disease. 0.5 to 1.5: the test shrugs; get a FibroScan or consider biopsy. Above 1.5: significant fibrosis is likely; above 2.0, cirrhosis is likely and screening for varices and liver cancer enters the plan.
APRI performs best in viral hepatitis and worst in fatty liver disease and alcohol-related disease, where other scores (FIB-4, NAFLD fibrosis score) fit better. For related liver lab interpretation, see our AST/ALT ratio guide and A/G ratio calculator.
When APRI misleads
Anything that raises AST without fibrosis inflates APRI: acute hepatitis flares, heavy recent drinking, muscle injury (AST lives in muscle too), and some medications. Anything that lowers platelets without liver disease deflates the denominator's meaning: ITP, chemotherapy, or lab artifact from clumped platelets.
Acute illness is the classic confounder: an AST of 800 during acute hepatitis gives a sky-high APRI that means inflammation, not cirrhosis. APRI is a chronic-disease tool; apply it to stable outpatients, not crashing inpatients.
APRI vs FIB-4: which to use
FIB-4 is APRI's main rival, adding age and ALT to the mix: age x AST / (platelets x sqrt(ALT)). It performs better in fatty liver disease, where APRI's cutoffs were never validated, and most NAFLD guidelines now list FIB-4 first. APRI keeps the edge in viral hepatitis, where its WHO cutoffs are entrenched.
In practice many clinics compute both, since they need the same blood draw. Agreement strengthens confidence; disagreement, usually APRI indeterminate with FIB-4 decisive or vice versa, pushes toward elastography. Two cheap scores beat one, and both beat guessing.
Elastography: the next step after APRI
When APRI lands indeterminate or high, vibration-controlled transient elastography (FibroScan) is usually next. A probe sends a shear wave through the liver; stiffer, more fibrotic tissue transmits it faster. The result in kilopascals maps to fibrosis stages: under 7 suggests minimal fibrosis, over 12 to 15 suggests cirrhosis, with the middle needing judgment.
It takes ten minutes, needs no sedation, and samples a volume 100 times larger than a biopsy needle. Obesity and narrow rib spaces degrade the reading, and acute inflammation stiffens the liver temporarily, so timing matters. But as a second-line test after APRI, it resolves most uncertainty without a needle.
Can fibrosis scores improve with treatment?
Yes, and watching APRI fall is one of the satisfying parts of liver care. Curing hepatitis C with direct-acting antivirals typically drops APRI substantially within a year as inflammation resolves and platelets recover. Suppressing hepatitis B, sustaining alcohol abstinence, and losing significant weight in NASH all move the score the right direction.
The caveat is what the improvement means. Early APRI drops mostly reflect cooling inflammation (AST falling) rather than true fibrosis regression, which takes years. A score falling from 2.5 to 1.2 after hepatitis C cure is excellent news, but the patient keeps cirrhosis surveillance until imaging confirms regression, because residual risk persists.
This is why hepatologists track APRI as a trend, not a verdict. Direction matters: steadily falling scores across two years tell a story of healing; a score stuck high despite treated disease suggests ongoing injury worth investigating. The number is a compass, and compasses are for journeys.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is a normal APRI score?
Below 0.5 suggests significant liver fibrosis is unlikely. There is no true 'normal' since it is a risk score, but lower is better.
What APRI indicates cirrhosis?
Above 2.0 suggests cirrhosis is likely, per WHO cutoffs. Between 1.5 and 2.0 suggests significant fibrosis short of cirrhosis.
How accurate is APRI?
Good at the extremes: it rules out and rules in fibrosis reasonably well. The 0.5 to 1.5 zone is indeterminate, and it is less accurate in fatty liver disease than in viral hepatitis.
What is the difference between APRI and FIB-4?
APRI uses AST and platelets only. FIB-4 adds age and ALT, and performs better in NAFLD. Both are first-line noninvasive fibrosis screens.
Can APRI replace liver biopsy?
No. It triages: low scores avoid biopsy, high scores may still need confirmation, and the middle zone needs elastography or biopsy to resolve.
Why do platelets drop in liver disease?
Portal hypertension enlarges the spleen, which traps platelets, and the failing liver makes less thrombopoietin, the hormone that drives platelet production.
Does alcohol affect APRI?
Yes. Recent heavy drinking raises AST and inflates the score without reflecting true fibrosis stage. Abstain before staging labs when possible.
How often should APRI be rechecked?
With routine liver labs, typically every 6 to 12 months in chronic liver disease, or as the hepatologist directs. Trends matter more than single values.