In a patient with steatosis and metabolic risk factors, the question is not whether there is fat but whether there is fibrosis, and FIB-4 answers the first part of that for nothing. It needs age, AST, ALT and platelet count - all of which you already have - and it is the recommended first gate in every current pathway.
The thresholds do different jobs. Below 1.3, advanced fibrosis is effectively excluded and the patient can be managed on metabolic risk in primary care with a repeat in one to three years. Above 2.67, the probability of advanced fibrosis is high enough to warrant specialist referral. Between the two is the indeterminate zone, which contains a substantial minority of patients and is where the second-line test belongs - transient elastography where available, or an ELF or similar patented panel where it is not.
Two cautions worth holding. FIB-4 performs poorly under 35 and over 65, and the upper cut-off should be raised in older patients to avoid over-referral. And a normal ALT excludes nothing: a significant proportion of patients with advanced fibrosis have transaminases inside the reference range, which is precisely why the score uses the platelet count.
- Calculate FIB-4 on anyone with steatosis and a metabolic risk factor - it needs no extra test
- Below 1.3, manage metabolic risk and repeat in one to three years
- Above 2.67, refer; between the two, arrange elastography or a second-line fibrosis panel
- Adjust interpretation at the extremes of age - the score performs poorly under 35 and over 65
- Do not use a normal ALT to rule out fibrosis
Why it matters
The commonest error in fatty liver is investigating the steatosis rather than staging the fibrosis, which is the only part that predicts outcome.
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