AST / ALT Ratio

AST and ALT are two enzymes that convert amino acids, and they come from the same tube of blood. The difference lies in where they sit. ALT sits almost only in the liver cells; AST also sits in muscles, heart and red blood cells, and in the liver cell it sits deeper, in the mitochondria, where alcohol releases it. So the ratio between the two tells something the single values do not: where the damage sits and what it looks like. In fatty liver, the most common liver condition, mainly ALT leaks and the ratio sits below 1. With alcohol mainly AST leaks, and alcohol also depletes the vitamin B6 with which ALT is measured, so the ratio rises, above 2 in the classic case. With muscle damage after hard training AST rises without the liver joining in, and the ratio is high while ALT is normal. And when a liver scars through years of strain, the ratio creeps upward, because the damaged cells release more AST. A ratio that shifts over the years from below 1 to above 1 is thereby an early sign that the liver is no longer just fatty. Your report shows the ratio as a bare number, without a unit. Healthy runs up to 1.3 in men and up to 1.7 in women, and most healthy people sit around 0.8 to 0.9. No test is needed for it: you divide your AST by your ALT, both in U/L.

The ratio is the value that with a raised ALT or AST answers the question you are really asking: is this fat, alcohol or muscles. Fatty liver gives an ALT higher than AST, with belly fat, high triglycerides and a low HDL alongside; that is the ratio below 1, and the treatment is weight loss and less sugar. Alcohol gives an AST that rises more than ALT, with a high gamma-GT and often a high MCV; that is the ratio above 2, and the treatment is cutting down. Muscles give a high AST with a normal ALT, after training, and that is not worth a treatment. The same single values, three different answers, and the division tells them apart. The second reason is time. Anyone who has a slightly raised ALT for years from fatty liver keeps, in the favourable case, a ratio below 1. If that ratio creeps up over the years to 1 and above, that is a sign the liver is starting to form scars, and that is the moment the FIB-4 score belongs with it. A ratio you follow over the years thereby says more than one result. And the third reason is what the ratio does not do. It was devised for the situation in which AST or ALT are already raised. If both sit within the range, the division yields a number that is about nothing: two normal values divided by each other say nothing about your liver.

Look first at whether AST or ALT falls outside your own lab's range. If not, leave the ratio alone; it says nothing then. A low ratio, below 1, with a raised ALT means ALT dominates. From common to rare: fatty liver with excess weight, a viral hepatitis that is recovering, and alcohol-related liver disease at an early stage, because there too a share sits below 1. Belly fat, triglycerides and gamma-GT say which. A high ratio, above 1 and certainly above 2, means AST dominates. In order: muscle damage after hard exertion, with a normal ALT and a high CK; alcoholic hepatitis, with a high gamma-GT; scarring in a chronic liver disease, in which the ratio rises over the years; and rarely a fulminant viral hepatitis. AST disappears from the blood faster than ALT, so a ratio that is high after muscle damage falls back within days. Set the ratio beside AST and ALT themselves, gamma-GT, bilirubin and ALP, and in an athlete beside CK. Have blood drawn on a rest day, because muscle damage lifts the ratio for a few days.