In one sentence
AST divided by ALT, which says which of the two liver enzymes is leading and, because the two leave the blood at different speeds, something about how fast and how recently the stress that raised them arrived.
Why it matters
Fernando De Ritis described the ratio in the 1950s as a feature of acute viral hepatitis, where ALT usually exceeds AST; others found the reverse in alcoholic liver injury; and the review that looked back on it found both readings too simple, because AST has a half-life of about 18 hours and ALT about 36, so the ratio reflects the time course and intensity of an injury as much as its cause, and because in chronic conditions, fatty liver among them, a ratio that has risen above 1 has been associated with more scarring (Botros 2013). The review also noted a methods point: whether the laboratory supplements its assays with pyridoxal phosphate shifts the two enzymes a little and can shift the ratio in people short of that vitamin.
What moves it
Whatever raised the enzymes, and when. Muscle work raises both, AST somewhat more, so a draw after a hard session tilts the ratio upward for a reason that is not the liver; an acute illness tilts it one way early and the other way later.
How to measure it well
From a liver panel on one draw under the panel's rules; the ratio of two enzymes from different draws means nothing. Same laboratory, because the assay supplementation point above differs between laboratories.
How Vitality Tracker uses it
Computed from one collection only and shown on the labs dashboard as context beside the enzymes, with the review's reading of the two directions stated as the review's. It is not scored, carries no working optimal, and prints on no report line of its own; FIB-4 is the figure the pre-visit report uses for the liver.
How far to trust the number
Calculated from two precise enzymes whose values depend on last week; the ratio is only as settled as they are.
Sources
- Botros M, Sikaris KA. The De Ritis ratio: the test of time. Clin Biochem Rev 2013;34:117–30. PMID 24353357
- Pettersson J, et al. Br J Clin Pharmacol 2008. doi:10.1111/j.1365-2125.2007.03001.x
- Vitality Tracker, Clinician report content specification (derived indices).