FIB-4

Fatty liver is present in one in four adults, and in most it stays at fat. In some the liver becomes inflamed over the years and forms scars, fibrosis, and that is the step that matters: a liver with fat recovers completely, a liver with many scars does not. The problem is that you do not see that in ALT and gamma-GT; those say the liver is under strain, not how much scar already lies there. FIB-4 fills that gap with four numbers you already have. Your age, because scars take years. Your AST and ALT, because a liver forming scars releases proportionally more AST. And your platelets, because a liver with many scars lets the blood from the gut through less well, so the spleen swells and traps platelets. Age times AST, divided by platelets times the square root of ALT, and the pattern that does not stand out in the single values becomes a number. The score is built to rule something out, not to prove something. Below 1.30 advanced scarring is unlikely, and the score is good at that. Above 3.25 it is likely enough to image the liver, with an elastography that measures the stiffness. In between the score deliberately says nothing, and that is not a shortcoming but the reason there are three bands.

FIB-4 is the score that turns fatty liver into an answerable question. Anyone with a slightly raised ALT and belly fat really wants to know only one thing: is this still fat, or are there scars already. A FIB-4 below 1.30 says it is almost certainly still fat, and fat disappears with weight loss, less sugar and exercise. That is the outcome the score was made for, and in most people with fatty liver it is the outcome. The second reason is that the score is free and already sits in your result. Your age, AST, ALT and platelets are in every ordinary panel, and the calculation takes ten seconds. Anyone who has their liver values measured yearly can calculate the score yearly and see whether it stays stable, which is the intention, or rises, which raises the question about the liver sooner. The third reason is that you have to know what the score is not. Your age is in the numerator, so the score rises with the years without anything changing in your liver; two people with the same blood get a different result at forty and at seventy, and above 65 the lower cut-off therefore sits higher in practice. Platelets fall through very different things than the liver too, and an AST that shoots up after hard training lifts the score with it. So a high score is a pattern to look further at, not a diagnosis.

A low FIB-4, below 1.30, means advanced scarring is unlikely. That is the outcome the score was made for, and with an ordinary liver picture at a younger age it is the outcome you expect. If you have fatty liver, this is the moment to clear the fat with lifestyle, before the score ever rises. A high FIB-4, above 3.25, means the four numbers together form a pattern that fits scarring, and then the liver should be imaged with an elastography. It does not mean the diagnosis is established. Look first back at the four numbers separately: an AST that shot up after training, platelets that are low for another reason, or simply being a year older, can lift the score without the liver having changed. Usually it is the first and rarely the last: getting older, fewer platelets, a shift between AST and ALT, and rarely real scarring. In between, from 1.30 to 3.25, the score deliberately says nothing. The question is then answered with an elastography or with a second score, and with the trend: a score that stays the same year on year is more reassuring than a score that rises.