The Fibrosis‑4 (FIB‑4) index, computed from age, aspartate aminotrasfertase (AST) and alanine aminotransferase (ALT) levels, and platelet count, was originally developed in 832 patients with HIV/hepatitis C virus coinfection to identify advanced liver fibrosis, achieving an area under the curve of 0.77 for distinguishing Ishak fibrosis stages 0–3 vs 4–6.¹ In that original work, a rule‑out threshold of 1.45 provided 70% sensitivity, whereas a rule‑in threshold of 3.25 offered 97% specificity. Subsequent applications have most often shifted toward respective cutoffs of 1.3 and 2.67. FIB‑4 has since been extensively validated across populations and liver disease contexts, and is now widely endorsed in clinical guidelines as a first‑line fibrosis test in primary care to identify individuals who warrant further liver fibrosis evaluation.^2,3 This includes patients with suspected steatotic liver disease, now the most prevalent chronic liver condition worldwide, affecting roughly one‑third of adults.⁴ At the same time, widespread fibrosis screening using FIB‑4 remains debated, given its suboptimal accuracy and the lack of long‑term trial evidence to confirm net benefit, cost‑effectiveness, and absence of unintended harms related to the screening process.⁴

In this issue of Polish Archives of Internal Medicine, Abu Baker et al⁵ add a novel and clinically useful perspective to this debate by showing that elevated FIB‑4 may function as a marker of multimorbidity and health care complexity, rather than a liver‑specific fibrosis signal alone. Using data from a large Israeli health maintenance organization covering approximately 1 million individuals, the authors identified 21 540 adults aged 40–80 years with FIB‑4 values equal to or greater than 2.67, and matched them 1:1 by age, sex, socioeconomic status, and ethnicity to individuals with persistently low FIB‑4 values (<⁠1.45 on all available measurements). This design mitigates age‑related confounding, given that age is embedded in FIB‑4 calculation.

The individuals with high FIB‑4 values carried a markedly higher baseline multimorbidity burden than the low–FIB‑4 controls, spanning cardiometabolic and kidney disease, immune‑mediated conditions, and cancer. The largest absolute prevalence gaps exceeded 15 percentage points (pp) for atrial fibrillation, congestive heart failure, and chronic kidney disease, with a striking over 20 pp difference for metastatic cancer and over 30 pp difference for pancreatic cancer. These marked baseline differences in cancer prevalence likely reflect the impact of systemic malignancy on transaminase levels and platelet counts, rather than indicating the capability of FIB‑4 to identify occult cancer. Accordingly, the findings should not be interpreted as support for using FIB‑4 as a cancer‑screening tool. Furthermore, over a median 6 years of follow‑up, high FIB‑4 was associated with substantially higher mortality (20.2% vs 9.7%) and more than 3‑fold higher annual health care costs, driven primarily by greater use of hospitalizations, procedures, specialty care, and surgery.

Notably, this divergence did not appear to be explained by differences in baseline prevalence of traditional population risk factors (eg, diabetes, hypertension, dyslipidemia, smoking, alcohol use, or physical activity) which were modest or absent between the groups. This pattern suggests that FIB‑4 may capture prognostic information beyond conventional risk profiling, although the present analysis did not formally assess incremental value using multivariable adjustment.

It is important to recognize that the non‑age components of FIB‑4 (AST and ALT levels, and platelet count) are influenced by extrahepatic and systemic processes, including inflammation, frailty, hematologic disorders, malignancy, medications, alcohol use, and intercurrent illness. Elevated FIB‑4 may therefore reflect systemic vulnerability as much as advanced liver fibrosis: a clinically useful insight, but also a potential source of misinterpretation if the score is treated as liver‑specific in isolation. Consistent with this interpretation, prior works have linked ALT and AST levels to all‑cause mortality beyond liver‑specific outcomes, likely reflecting the same broader, systemic signal that high FIB‑4 appears to capture in this study.^6,7 Whether FIB‑4 adds extrahepatic prognostic information beyond its individual components remains unknown.

Study limitations include restricted granularity in alcohol exposure and potential selection bias due to opportunistic ascertainment of FIB‑4 from routine laboratory testing rather than standardized screening. In addition, the stringent control group definition (FIB‑4 <⁠1.45 on all available measurements) may preferentially select individuals with persistently favorable laboratory profiles and lower underlying illness burden. Conversely, in some cases, high FIB‑4 may have been captured during intercurrent or acute illness, potentially amplifying contrasts between the groups. However, these considerations do not negate the value of the study for signal detection, but they shape interpretation—particularly in the absence of data regarding fibrosis staging, cirrhosis prevalence, and liver‑related outcomes, and with the intermediate “gray zone” (FIB‑4, 1.45–2.66) left unexamined, limiting insight into risk gradients and how to best act in the case of intermediate scores.

Taken together, Abu Baker et al⁵ convincingly demonstrated that elevated FIB‑4 functions as a marker of systemic vulnerability that extends well beyond hepatology. They invited a reframing of FIB‑4 as a simple, widely available marker of multisystem morbidity, health care complexity, and increased mortality, rather than merely a surrogate for liver fibrosis severity. While this broader signal could strengthen the rationale for using FIB‑4 in screening—within and potentially beyond liver pathways—future studies must establish whether identifying individuals with high FIB‑4 values can be translated into targeted actions that meaningfully reduce multimorbidity, health care utilization, costs, and premature mortality. Pragmatically, an initial response—alongside appropriate liver fibrosis evaluation—may be to confirm persistence of the laboratory abnormalities driving FIB‑4, review reversible contributors (medications, alcohol use, intercurrent illness), and undertake a structured assessment of cardiometabolic risk and kidney function. Framed this way, an elevated FIB‑4 can serve as a simple “clinical flag” that prompts proportionate, patient‑centered evaluation and targeted risk modification, without defaulting to automatic multidisciplinary referral cascades.