Liver Function Calculator — AST/ALT, APRI, FIB‑4

How to Use Liver Function Calculator — AST/ALT, APRI, FIB‑4

1. Step 1: Enter Age

   Type your age in years (18+) from your chart or memory.

2. Step 2: Add Enzymes

   Enter AST and ALT in U/L from the same lab report (same date).

3. Step 3: Add Platelets

   Enter platelet count in 10^9/L as printed on your report.

4. Step 4: Set AST ULN

   Use your lab’s AST upper limit of normal (ULN). Default is 40 U/L.

5. Step 5: Calculate & Review

   Tap Calculate to see AST/ALT ratio, APRI, and FIB‑4 with simple guidance.

Key Features

• AST/ALT ratio (De Ritis)
• APRI fibrosis index
• Age‑adjusted FIB‑4
• Custom AST ULN
• Mobile‑first inputs

Understanding Results

Using the Liver Function Calculator

The liver function calculator summarizes AST/ALT ratio, APRI, and FIB‑4 from your labs to provide clear, non‑diagnostic context.

Formula

AST/ALT ratio = AST ÷ ALT (both in U/L from the same blood draw). It is a simple ratio that describes relative changes in these enzymes.

APRI = (AST ÷ AST ULN) × 100 ÷ platelets (10^9/L). It estimates the probability of significant fibrosis using enzyme elevation relative to normal and platelet count.

FIB‑4 = (Age × AST) ÷ (Platelets × √ALT). It combines age and common labs to stratify advanced fibrosis risk. For adults over 65, a higher “low‑risk” threshold is often used.

Reference Ranges & Interpretation

• AST/ALT ratio: < 1 can be seen in many benign states; ≈1 is ambiguous; ≥2 has been described in patterns seen with alcoholic hepatitis or advanced fibrosis, but is not specific.
• APRI: <0.5 low probability of significant fibrosis; 0.5–1.5 indeterminate; ≥1.5 suggests significant fibrosis (cutoffs vary by source).
• FIB‑4: For age ≤65: <1.3 low, 1.3–2.67 indeterminate, >2.67 high. For age >65: <2.0 low, 2.0–2.67 indeterminate, >2.67 high.

Assumptions & Limitations

Scores are screening aids and not diagnoses. Acute illness, medications, alcohol, strenuous exercise, hemolysis, and non‑liver sources of AST can change results. Always interpret alongside the absolute enzyme values, your lab’s reference ranges, symptoms, imaging, and clinician guidance.

Complete Guide: Liver Function Calculator — AST/ALT, APRI, FIB‑4

Use our liver function calculator to interpret liver labs with AST/ALT ratio, APRI, and FIB‑4. Enter age, enzymes, platelets, and AST ULN for clear results. It keeps everything transparent: you provide age and three common labs (AST, ALT, and platelets) plus your lab’s AST upper limit of normal (ULN). We return the AST/ALT ratio, APRI, and FIB‑4 — three widely discussed non‑invasive scores that help organize what your numbers may mean.

Remember that a calculator is a planning tool, not a diagnosis. Your clinician will weigh these scores alongside symptoms, exam findings, medications, alcohol exposure, viral hepatitis status, metabolic risks, and imaging. Use this page to better understand what you see on your report and to prepare clear questions for your next visit.

What this tool is and isn’t

The goal of this liver function calculator is to turn a few numbers from your lab report into structured information you can understand. It uses three non‑invasive indicators commonly referenced in clinical discussions:

• AST/ALT ratio (De Ritis): a simple division, AST ÷ ALT, showing relative change between these enzymes.
• APRI: (AST ÷ AST ULN) × 100 ÷ platelets, which estimates probability of significant fibrosis using enzyme elevation relative to normal and platelet count.
• FIB‑4: (Age × AST) ÷ (Platelets × √ALT), a composite index often used in primary‑care pathways to flag advanced fibrosis risk.

These measures are decision aids. They are not definitive tests, and they can be influenced by temporary conditions such as acute illness, exercise, or medications. For example, AST is also present in skeletal muscle, so hard workouts or muscle injury may raise AST and shift your AST/ALT ratio without a primary liver problem. Platelets may be low for many reasons beyond liver disease. That is why the calculator highlights ranges and context, not binary diagnoses.

Inputs and units you’ll need

You only need four numbers and one reference value, all from the same blood draw:

1. Age in years.
2. AST in U/L (units per liter).
3. ALT in U/L.
4. Platelets in 10^9/L (sometimes written as ×10^9/L).
5. AST ULN (your laboratory’s upper limit of normal for AST) — 40 U/L is common, but your lab’s exact value wins.

Consistency matters. Use results printed on the same report and do not mix numbers from different dates. If your lab uses different reference intervals than you’ve seen online, simply enter the ULN shown on your report; this keeps APRI tailored to your testing method.

How AST/ALT, APRI, and FIB‑4 are calculated

AST/ALT ratio is straightforward: divide AST by ALT (both U/L). Values less than 1 are common and can be seen in many benign states. A ratio close to 1 is ambiguous and needs context. Ratios at or above 2 have been described in patterns seen with alcoholic hepatitis or advanced fibrosis, but this is not specific.

APRI compares AST to the upper limit of normal and adjusts for the platelet count: (AST ÷ AST ULN) × 100 ÷ platelets. In general, lower APRI suggests lower probability of significant fibrosis; higher APRI suggests increased probability. Many pathways use <0.5 as low probability, 0.5–1.5 as indeterminate, and ≥1.5 as suggestive of significant fibrosis, though thresholds vary by source.

FIB‑4 = (Age × AST) ÷ (Platelets × √ALT). For adults up to age 65, a FIB‑4 below 1.3 is often considered low risk of advanced fibrosis, 1.3–2.67 indeterminate, and above 2.67 higher risk. In adults over 65, some pathways use a more conservative “low‑risk” cutoff of 2.0 before calling results indeterminate. This calculator applies the age‑adjusted low‑risk threshold automatically.

Interpreting your results

Use the three outputs together and read them next to the absolute enzyme values on your report. For example, a mildly elevated ALT with an AST/ALT ratio below 1 and a low APRI and FIB‑4 may point toward a lower probability of advanced fibrosis. In contrast, elevated AST and ALT with a ratio near or above 2, an APRI above 1.5, and a FIB‑4 above 2.67 are all signals that additional evaluation may be appropriate.

• Low‑risk profile: APRI < 0.5 and FIB‑4 below the age‑adjusted low cutoff (1.3 if ≤65; 2.0 if >65) with modest enzyme elevations.
• Indeterminate: APRI 0.5–1.5 and FIB‑4 between the low and high cutoffs (1.3–2.67 or 2.0–2.67 if >65). Repeat testing, trend review, or ultrasound may be suggested.
• Higher‑risk profile: APRI ≥ 1.5 or FIB‑4 > 2.67, especially if the AST/ALT ratio is ≥ 2 and platelet count is low. Consider discussing next steps with your clinician.

AST/ALT, APRI, and FIB‑4 at a glance

Think of these outputs as traffic lights for risk, not diagnoses. A low APRI and low FIB‑4, together with modest enzyme elevations, usually point toward lower short‑term concern for advanced fibrosis. Indeterminate ranges invite a closer look at trends, ultrasound, or repeat labs after a period of steady routines. High‑risk results are a cue to connect with your clinician for next steps. Use this liver function calculator to organize the numbers, then rely on professional judgement for decisions.

If your clinician is considering cirrhosis severity or transplant prioritization, other tools may be used. For example, the Child‑Pugh calculator summarizes overall function using albumin, bilirubin, INR, ascites, and encephalopathy. The MELD score calculator estimates short‑term mortality risk in advanced disease. Those tools serve different purposes than non‑invasive screening indices like APRI or FIB‑4.

Common scenarios and examples

1) Mild enzyme elevations after strenuous exercise. If you recently completed a hard workout, AST may rise more than ALT because AST is present in muscle. The AST/ALT ratio can shift upward even when the liver is not the main source of the change. In such cases, APRI and FIB‑4 may still read low risk if platelets are normal and the absolute enzyme values are only slightly elevated. Time and repeat testing often clarify whether this is a transient pattern.

2) Metabolic risk and fatty liver. In people with metabolic syndrome, diabetes, or obesity, ALT may be higher than AST (ratio <1), but the scale of elevation and trends matter. A low FIB‑4 helps rule out advanced fibrosis in many primary‑care pathways. Our dedicated AST/ALT ratio calculator can help you focus on the ratio alone if needed, but FIB‑4 often adds more context.

3) Suspected alcohol‑related liver disease. When the ratio is around 2 or higher and enzymes are elevated, clinicians sometimes describe this as a pattern seen with alcohol‑related injury. It is not specific. Platelets, bilirubin, albumin, and INR — none of which are used by APRI or FIB‑4 — are often reviewed alongside history, imaging, and exam. If alcohol is a concern, our alcohol units calculator can help you quantify intake in standardized units.

4) Chronic viral hepatitis or long‑standing disease. Non‑invasive scores may trend upward over time as fibrosis advances, but acute flares can also raise enzymes suddenly. Consistency in timing and using the same lab help with interpretation. Advanced assessments may include elastography or biopsy, which are beyond this tool’s scope.

Lifestyle context and liver health

Many factors that support overall health also support the liver. Maintaining a healthy weight, moderating alcohol, managing diabetes and lipids, reviewing medications and supplements with your clinician, staying up‑to‑date on vaccinations (such as hepatitis), and building a regular sleep and activity routine all contribute to better outcomes. None of this replaces a tailored plan from a professional who knows your history, but it shows why trends in labs are often read in the context of day‑to‑day habits.

Beyond the liver, kidney function and general metabolic health can influence decision making in advanced disease. If you’re tracking broader health markers, our kidney function calculator and A1C calculator provide quick context for related labs. For weight and nutrition planning, you can also browse our calculators index to find tools that fit your goals.

When to seek medical care

Seek medical care promptly if you have yellowing of the skin or eyes (jaundice), dark urine, pale stools, confusion, easy bruising, severe abdominal pain, vomiting blood, or black tarry stools. These symptoms can signal urgent problems and warrant immediate evaluation. Even without alarm symptoms, persistently high enzymes, rising scores, or a high‑risk FIB‑4 (>2.67) are good reasons to follow up with a clinician. Never start or stop medicines based solely on a score from a calculator.

Related tools and next steps

• AST/ALT Ratio Calculator: Focus on the De Ritis index alone with a compact UI and interpretation notes.
• Child‑Pugh Calculator: Summarizes cirrhosis severity using labs and clinical findings.
• MELD Score Calculator: Estimates short‑term mortality risk used in transplant triage.
• Alcohol Units Calculator: Convert drinks to standardized units to better quantify exposure.
• Kidney Function Calculator: Context for renal labs that may interact with liver care in advanced disease.

To keep everything organized, bookmark our full calculators index. When you are ready, return to the top of this page to enter your numbers or update them after a new lab draw.

Guide FAQs

Do I need fasting for liver enzymes? Most labs do not require fasting for AST/ALT. The bigger issue is using results from the same draw and following your lab’s instructions for timing and medications.

Why use my lab’s AST ULN? APRI calibrates AST to your lab’s “normal” range. Because reference intervals vary by method and population, the ULN printed on your report is the best anchor for your calculation.

What if my scores disagree? That can happen. APRI and FIB‑4 emphasize different aspects of disease biology (enzyme elevation vs. platelet trends and age). Clinicians often repeat labs, review trends, and add imaging when scores conflict.

Where can I read more? For general background, large public sources such as the U.S. National Library of Medicine (MedlinePlus) and professional society guidelines (e.g., AASLD) provide helpful overviews. Always use official health sites for evidence‑based information.

This guide is informational and does not provide medical advice. It does not replace diagnosis, clinical judgment, or personalized care.

Frequently Asked Questions