‘CAP’ Quantification of Liver Fat Not Reliable for Routine Use | Nutrition Fit



NEW YORK (Reuters Health) – Ultrasound-based controlled attenuation parameter (CAP), a noninvasive tool for assessment of hepatic steatosis, should be used with caution because while results are reliable in patients with viral hepatitis, that’s not the case for non-alcoholic fatty liver disease (NAFLD), researchers say.

CAP was originally available only with a probe for lean individuals – the M probe. The XL probe, designed for patients with a higher body mass index (BMI), was introduced more recently. Conflicting findings regarding the XL probe’s diagnostic performance and optimal CAP prompted the current patient-level meta-analysis.

“In a complete clinical work-up of patients with chronic liver disease, the CAP value can contribute to decisions taken in clinical management,” Drs. David Petroff of the University of Leipzig and Thomas Karlos of Leipzig University Medical Center told Reuters Health in a joint email. “The clinician should be aware, however, that substantial uncertainties regarding steatosis grade require that the CAP measurement alone should not generally be the determining factor when choosing treatment pathways.”

“Our individual-patient data meta-analysis (showed) that the diagnostic properties of CAP depend on the cause of the liver disease, factors associated with body weight, and the frequency of people having steatosis,” they said. “Thus, the CAP measure requires careful interpretation by a trained physician.”

“The XL probe permits hepatic fat quantification in a larger proportion of patients with obesity, but in doing so opens up Pandora’s box,” they added. “By extending the accessible population, the scope of liver diseases and comorbidities is increased considerably, and along with it, the complexity of understanding and diagnosing ‘fatty liver.'”

As reported in The Lancet Gastroenterology and Hepatology, the team searched the literature from inception through April 2019 for studies with biopsy-controlled data on the use of CAP for non-invasive grading of steatosis.

“Previous analyses have shown good diagnostic performance in patients with viral hepatitis using the M probe, and the current analysis suggests only a slight deterioration when extending the population to (viral hepatitis) patients with a higher BMI and use of the XL probe,” the researchers said.

NAFLD patients, the main group assessed with the XL probe, were analyzed separately.

Sixteen controlled studies and individual data from 13 papers involving 2,346 patients (mean age, 46.5; 51% women) from 20 centers in nine countries were included. Of the 2,283 patients with BMI data, 29% were normal weight (BMI <25 kg/m²), 23% were overweight (25 to <30), and 47% were obese (30 or higher).

Fifty-four percent had NAFLD; 20%, viral hepatitis; 12%, alcohol-associated liver disease; and 13%, other liver disease etiologies.

According to the authors, the XL probe was correctly chosen for use in 1,050 patients, of whom 930 (89%) had NAFLD. Among those with NAFLD, the AUCs were 0.819 for steatosis grade S0 versus S1 to S3 and 0.754 for S0 to S1 versus S2 to S3.

“The AUC for detection of any steatosis (S1 to S3) is better at 0.819, but S0 cases are heavily influenced by patients scheduled for bariatric surgery,” the authors note. “Overall, the diagnostic performance of CAP in patients undergoing bariatric surgery is better than for the typical patient with NAFLD.”

Taken together, CAP values were independently affected by etiology, diabetes, BMI, aspartate aminotransferase, and sex. “Even with the XL probe, CAP cannot grade steatosis in patients with NAFLD adequately,” the authors state.

Dr. Giovanna Ferraioli of the Medical School University of Pavia, Italy, author of a related editorial, commented in an email to Reuters Health, “Given the uncertainty about the cutoff value for the detection of liver steatosis, probably related to the spectrum effect in the published studies, CAP is not ready yet to be used as a screening tool for the diagnosis of steatosis in the primary care settings.”

“On the other hand,” she said, “when assessing the performance of new noninvasive tools for the detection and grading of liver steatosis, liver biopsy is not the best reference to compare the results with, given the very small size of the biopsy specimen and the dynamic nature of liver fat content.”

“Quantitative assessment of liver steatosis with other ultrasound systems is an interesting research field with very promising results, but it’s too early for use in everyday clinical practice,” she concluded.

SOURCE: https://bit.ly/3rtuxr4 and https://bit.ly/36TSArx Lancet Gastroenterology and Hepatology, online January 15, 2021.


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