How this instrument works
AST and ALT are both enzymes that leak out of injured liver cells, but not in the same amounts for every kind of injury. Alanine aminotransferase (ALT) lives mostly in the liver, while aspartate aminotransferase (AST) also turns up in heart and skeletal muscle, and the two rise in different proportions depending on what is damaging the liver. Dividing AST by ALT gives the De Ritis ratio, named for Fernando De Ritis, who with colleagues Coltorti and Giusti described the pattern in a 1957 paper, "An enzymic test for the diagnosis of viral hepatitis: the transaminase serum activities," published in Clinica Chimica Acta (volume 2, pages 70-74), showing the figure characteristically inverted in viral hepatitis.
MedlinePlus's AST and ALT test pages describe each enzyme individually as a marker of liver — and, for AST, muscle or heart — injury, and StatPearls' clinical reference on the ALT test covers how the two are read together in practice. As a rough guide, a result below 1 is common in viral hepatitis and fatty liver disease, a figure near 1 is fairly nonspecific, and a number above roughly 2 — especially when both enzymes are only mildly raised — is the pattern classically taught for alcohol-related liver injury, partly because heavy alcohol use blunts ALT production more than it blunts AST.
The comparison was devised before more specific liver tests existed, and it works best as one clue among several rather than a stand-alone read. Extremely elevated enzymes, certain medications, and non-liver sources of AST can all distort it, and plenty of liver disease produces enzyme patterns that do not sort neatly by this single number. A clinician weighs it together with the absolute enzyme levels, other liver tests such as bilirubin and alkaline phosphatase, imaging, and patient history — this instrument computes the figure; it does not replace that judgment.
- Enter AST in U/L from your liver panel (also labeled SGOT on older reports).
- Enter ALT in U/L from the same panel (also labeled SGPT).
- Read the AST/ALT ratio (De Ritis ratio): the calculator divides AST by ALT directly.
- Weigh the figure alongside how far above normal each enzyme individually sits — a ratio built from two barely-elevated enzymes carries different weight than the same ratio from two markedly elevated ones.
Worked example — three liver panels
AST 40 U/L, ALT 20 U/L. Divide directly: 40 ÷ 20 = 2. A result of exactly 2, particularly when both enzymes sit only mildly above their own reference ranges, is the textbook pattern for alcohol-related liver injury rather than a viral cause — one clue, not a confirmed diagnosis.
AST 30 U/L, ALT 90 U/L. Here ALT runs three times AST: 30 ÷ 90 ≈ 0.33. A figure well under 1, with ALT dominating, is the pattern more typical of viral hepatitis or fatty liver disease, where ALT tends to climb faster than AST.
AST 50 U/L, ALT 50 U/L. Equal values divide to exactly 1 — a genuinely ambiguous result. On its own a number of 1 does not point clearly toward either pattern above; it needs the surrounding clinical picture, the absolute enzyme levels, other liver tests, and history, to mean anything.
Questions
What is the De Ritis ratio used for?
It is a rough pattern-read on two liver enzymes, AST and ALT, that can hint at what kind of liver injury is present — alcohol-related injury classically shows a higher figure, while viral hepatitis and fatty liver disease more often show a lower one. It was first described by Fernando De Ritis and colleagues in 1957 and is still taught as a quick first read on a liver panel, though it is never used alone.
What counts as a high or low De Ritis ratio?
As a general guide, above roughly 2 is the pattern associated with alcohol-related liver injury, especially when both enzymes are only mildly elevated; below 1 is more typical of viral hepatitis or fatty liver disease; and a figure near 1 is fairly nonspecific. Exact cutoffs vary between clinical sources, and none of them act as a hard diagnostic line.
Why does alcohol raise AST more than ALT?
Chronic heavy alcohol use damages the mitochondria where AST is partly produced, and it also depletes vitamin B6 (pyridoxal phosphate), which ALT production depends on more heavily than AST does. The combined effect is that ALT climbs less than AST in alcohol-related liver injury, pushing the figure above 1 and often above 2.
Is a result of exactly 1 abnormal?
Not necessarily — equal AST and ALT is common and, by itself, does not point clearly toward either the alcohol-associated or the viral or fatty-liver pattern. Whether it means anything depends on whether the absolute enzyme levels are elevated at all, and on the rest of the clinical picture surrounding them.
Can this ratio diagnose the cause of my liver enzyme results?
No. It performs one division on two lab values and reports where that falls relative to commonly cited patterns. Confirming an actual cause takes a clinician reviewing the absolute enzyme levels, other liver tests, imaging, alcohol and medication history, and symptoms alongside this figure — it is a starting clue, not a diagnosis.
What units does this calculator expect for AST and ALT?
Both in U/L (units per liter), the standard units printed on most liver panels. Since the figure is a plain division of one value by the other, the units cancel and the result is unitless regardless of which lab reported the numbers, as long as both are given in the same units.
References
- MedlinePlus — AST Test
- MedlinePlus — ALT Blood Test
- StatPearls — Alanine Aminotransferase (ALT) Test
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.