AST/ALT (De Ritis) Ratio Calculator

Understanding the AST/ALT (De Ritis) ratio calculator — concept and principle

The AST/ALT ratio, also called the De Ritis ratio after the Italian physician Fernando De Ritis who described it in 1957, divides one liver enzyme by another. It is used alongside the absolute enzyme levels to suggest which kind of liver injury is more likely when liver tests come back abnormal.

How it is calculated

AST/ALT ratio = AST (U/L) ÷ ALT (U/L)

Both values should come from the same blood sample and the same laboratory. The calculator labels a ratio above 2, below 1 or between 1 and 2.

The principle

AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are enzymes released when liver cells are damaged. ALT is found mainly in the liver, while AST is also present in heart, skeletal muscle and red blood cells, and inside liver cells it sits partly in the mitochondria. In most fatty liver disease and acute viral hepatitis, ALT rises more than AST, so the ratio falls below 1. In alcohol-related liver disease, alcohol damages mitochondria and the body is often short of vitamin B6, which ALT needs, so AST rises more and the ratio often exceeds 2. As liver fibrosis advances to cirrhosis, AST clearance falls and the ratio tends to rise above 1 regardless of cause.

Worked example

1. Inputs: AST 35 U/L, ALT 40 U/L.
2. Ratio = 35 ÷ 40 = 0.875, shown as 0.88.
3. Because 0.88 is below 1, the calculator shows the pattern ratio < 1 is common in fatty liver / viral hepatitis.

How to read the result

The ratio means little if both enzymes are within the lab's normal range, as in this example where the values are near typical upper limits. It becomes useful when enzymes are clearly raised: a ratio below 1 points towards fatty liver or viral hepatitis, above 2 raises the question of alcohol, and a rising ratio over time in chronic liver disease can signal progressing fibrosis. Doctors combine it with history, imaging and other tests such as GGT, bilirubin and platelets.

Common mistakes

• Interpreting the ratio when both enzymes are normal.
• Forgetting that hard exercise or muscle injury can raise AST without any liver problem.
• Comparing values from different labs, whose reference ranges and methods differ.

Frequently asked questions

What are normal AST and ALT levels?

Reference ranges are set by each laboratory and differ by sex and method, so check the range printed on your report.

Can medicines change AST and ALT?

Yes. Many drugs and supplements can raise liver enzymes, which is why doctors ask what you take.

Does a normal ratio rule out liver disease?

No. Fatty liver and even cirrhosis can occur with normal or near-normal enzymes.

Sources: De Ritis F, Coltorti M, Giusti G. An enzymic test for the diagnosis of viral hepatitis: the transaminase serum activities. Clin Chim Acta 1957;2(1):70–74.