AST/ALT Ratio (De Ritis Ratio)

What the AST/ALT ratio is and when it is used

The AST/ALT ratio is the activity of aspartate aminotransferase (AST, formerly SGOT) divided by the activity of alanine aminotransferase (ALT, formerly SGPT). It is called the De Ritis ratio after Fernando De Ritis, who described it with Coltorti and Giusti in 1957 while studying transaminases in viral hepatitis.

Both enzymes are located inside cells and rise in the blood when there is injury. ALT is more concentrated in the liver. AST exists in the liver, but also in skeletal muscle, heart, kidney and red blood cells. The proportion between them changes according to the type of injury, the location inside the cell and the clearance time: according to the review by Botros and Sikaris (2013), the half-life of AST is about 18 hours and that of ALT about 36 hours.

In practice, the ratio is used when transaminases are already abnormal, to suggest a pattern and guide the workup. Since AST also comes from muscle, it is worth checking the CK-MB relative index as well when muscle injury is suspected.

How to calculate the AST/ALT ratio in the calculator

The calculator asks for two values from the same report, both greater than zero:

1. AST (SGOT), in U/L.
2. ALT (SGPT), in U/L.

The tool divides AST by ALT and shows the result with two decimal places, unitless, because the units cancel out. It then describes the pattern of the range the value falls into, with the source: above 2, from 1 to 2 (inclusive) or below 1. The range is decided on the unrounded value.

Values equal to or below zero, or above 100,000 U/L, produce an error message.

Three precautions before entering values:

• both enzymes must come from the same sample and the same laboratory;
• order matters: AST in the numerator, ALT in the denominator;
• U/L and IU/L are the same unit; results in µkat/L must both be converted the same way, or the ratio will be wrong.

De Ritis ratio formula and definition of terms

The De Ritis ratio is a simple ratio between two enzyme activities measured in the same sample.

De Ritis ratio = AST (U/L) ÷ ALT (U/L)

• AST (SGOT): aspartate aminotransferase, present in the cytoplasm and mitochondria of hepatocytes, muscle and other tissues.
• ALT (SGPT): alanine aminotransferase, predominantly cytoplasmic and more liver-specific.
• Result: a dimensionless number. A value of 1 means equal activities.

The formula has no constants or corrections. Therefore, the result depends directly on the method for each enzyme. Botros and Sikaris (2013) note that the IFCC recommends adding pyridoxal-5′-phosphate (vitamin B6) to transaminase reagents. Methods without this cofactor may underestimate activity in people with B6 deficiency, such as some patients with alcoholism, older adults and cancer patients. According to the same review, the effect on the ratio is usually mild, but it exists.

Worked example of the AST/ALT ratio

Consider hypothetical data, only to check the calculation: AST of 120 U/L and ALT of 50 U/L, in the same sample.

1. Divide AST by ALT: 120 ÷ 50 = 2.4.
2. With two decimal places: AST/ALT ratio = 2.40.

The calculator returns 2.40 for these data and, since the value is greater than 2, describes the pattern of the upper range: Cohen and Kaplan (1979) found a ratio above 2 in 70% of cases of alcoholic liver disease and in 4% of viral hepatitis cases.

Now swap the enzymes: AST of 50 U/L and ALT of 120 U/L. The ratio becomes 50 ÷ 120 = 0.42, in the range below 1. The example shows how swapping the fields completely changes the reading.

Neither result is diagnostic. A ratio of 2.40 can also appear because of recent muscle injury, since AST leaves the muscle, or because of other causes cited in the literature. The next step is always the clinical context, with history of alcohol use, medications, serologies, imaging and, when indicated, total CK.

How to understand the result: ranges and what studies say

The calculator uses three ranges: above 2, from 1 to 2 and below 1. The texts describe the published pattern, without pointing to a diagnosis.

The two extreme ranges come directly from the literature:

• Above 2: Cohen and Kaplan (1979) observed a mean ratio of 2.85 in alcoholic hepatitis and alcoholic cirrhosis, and concluded that a ratio greater than 2 is highly suggestive of these conditions. It occurred in 70% of these patients, versus 4% in viral hepatitis.
• Below 1: in acute viral hepatitis, the ratio is usually well below 1, typically between 0.5 and 0.7, according to Botros and Sikaris (2013).

The intermediate range is heterogeneous. The same review points out that a ratio above 1 in chronic hepatitis B and C is associated with fibrosis, and notes that most patients with alcoholic liver disease have a ratio below 2. There is no accepted reference interval for the ratio in healthy people. Interpretation is the responsibility of the professional, with the full clinical picture.

Common errors and verification checklist

The ratio is simple, but some common errors make the number misleading.

• Calculating with normal transaminases: the ratio has little value when both enzymes are within the reference range; small analytical variations change the result a lot.
• Swapping the fields: ALT in the numerator produces the inverse of the ratio.
• Mixing laboratories or dates: different methods, with or without pyridoxal phosphate, shift the ratio.
• Ignoring the muscle origin of AST: intense exercise, trauma, intramuscular injections and myopathies raise AST and the ratio.
• Ignoring hemolysis: red blood cells contain AST, and hemolyzed samples can raise measured AST.
• Reading the range as a diagnosis: the calculator's texts describe published patterns, not conclusions.

Checklist:

1. Are AST and ALT from the same sample and the same method?
2. Is at least one of the enzymes abnormal?
3. Is AST in the numerator?
4. Is there a reason for muscle injury? If so, was CK measured?
5. Was the result read together with the clinical picture and other liver tests?

Limitations of the AST/ALT ratio and comparison with other markers

The AST/ALT ratio does not diagnose any disease on its own. It summarizes two enzymes in a single number and loses information about magnitude: a ratio of 2 can come from 40/20 U/L or from 800/400 U/L, clinically different situations.

Other limitations described in the review by Botros and Sikaris (2013):

• the ratio changes over the course of the illness, because AST is cleared faster than ALT;
• in acute muscle injury the ratio rises, but it can fall to near 1 within a few days;
• other conditions, such as acetaminophen poisoning, can take the ratio above 2;
• in hepatic steatosis, there may be fibrosis with normal transaminases.

Compared with other tests, the ratio is a complement. Gamma-GT and alkaline phosphatase help separate cholestatic patterns. Total CK confirms muscle origin. Imaging and fibrosis scores assess liver structure. When there is jaundice, bilirubin can interfere with creatinine measurement, the subject of the bilirubin-corrected creatinine page. Since fatty liver disease is associated with insulin resistance, the HOMA-IR index often enters the same workup.

Frequently asked questions about the AST/ALT ratio (De Ritis ratio)

References

1. 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):70-4. View
2. Cohen JA, Kaplan MM. The SGOT/SGPT ratio: an indicator of alcoholic liver disease. Dig Dis Sci. 1979;24(11):835-8. View
3. Botros M, Sikaris KA. The De Ritis ratio: the test of time. Clin Biochem Rev. 2013;34(3):117-30. View