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Reuters Health Information (2013-01-16): Critical flicker frequency helps diagnose minimal hepatic encephalopathy


Critical flicker frequency helps diagnose minimal hepatic encephalopathy

Last Updated: 2013-01-16 15:59:22 -0400 (Reuters Health)

NEW YORK (Reuters Health) - A patient's ability to distinguish a steady light from a flickering light can be used to diagnose minimal hepatic encephalopathy (MHE), a new meta-analysis indicates.

So-called critical flicker frequency (CFF) provides high specificity and moderate sensitivity for diagnosing MHE, the U.K. study team reports.

"CFF is an easy to use objective test that can be administered in a busy clinic without recourse to a neuropsychological consultation," Dr. Simon D. Taylor-Robinson from Imperial College London told Reuters Health. "The test is simple and reproducible and applicable anywhere without the need for literacy, numeracy, or proficiency in English."

CFF measures the frequency at which the patient perceives that a fused/single light becomes a flickering light during a stepwise decrease in frequency from 60 to 25 Hz.

Dr. Taylor-Robinson and colleagues performed a systematic review and meta-analysis of nine published studies of CFF, involving 622 patients, to assess its diagnostic accuracy in detecting MHE.

They reported January 7 online in Alimentary Pharmacology & Therapeutics that only four of the studies were of high quality; the others were all of low quality.

Four studies used the Psychometric Hepatic Encephalopathy Score (PHES) as their gold standard; five used other tests.

The pooled data from all nine studies yielded 61% sensitivity, 79% specificity, a 3.5 positive likelihood ratio, a 0.46 negative likelihood ratio, and a 10.9 diagnostic odds ratio.

There was significant heterogeneity in all measures, but there was no significant publication bias, according to the authors.

"CFF was effective in discriminating patients with MHE from those without MHE and therefore has potential as a screening tool, either to be used prior to current psychometrics tools, or to be used alongside these tests, but not as a replacement for them given the risk of false negative results," the researchers concluded.

Dr. Taylor-Robinson said CFF could be used at all centers, including those that used the PHES to diagnose MHE.

"We haven't currently planned further studies using CFF," Dr. Taylor-Robinson said, "but would think that a formal validation against a battery of psychometric tests (PHES, Cogstate, SCANTEST) and imaging (fMRI, MR spectroscopy) is indicated."

Dr. Praveen Sharma from the Institute of Liver and Biliary Sciences, Delhi, India has published research on CFF and MHE. Dr. Sharma told Reuters Health, "I think CFF should be the first test to screen for MHE and supplemented by PHES if needed, as it easily can be done in outpatient department and is user friendly."

Dr. Sharma recommends that physicians "use PHES as the standard for MHE and validate CFF in your own population for diagnosing MHE."


Aliment Pharmacol 2013.

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