Critical flicker frequency analysis (CFF)

CFF defines the frequency at which a proband perceives the apparent transition from fused light to a flickering one, known as the critical flicker frequency. Pathological threshold for minimal HE: ≤ 39 Hertz. Using CFF means HE can be staged and monitored over time.

This graph shows how CFF can be used in the diagnosis of HE.1

It has been demonstrated there is a close correlation between CFF and severity of HE. In addition there is a statistically significant correlation between CFF and psychometric tests, good correlation between CFF and arterial ammonia concentration. Importantly results are not dependent on the patient’s educational level and there are no training effects.


The method and results could be affected by age of patients.

CFF equipment

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1. Kircheis G, Wettstein M, Timmermann L et al. Critical flicker frequency for quantification of low-grade hepatic encephalopathy. Hepatology. 2002;35(2):357-66.