Mortality Rate for Chronic Liver Disease Underestimated

Christina Bennett

November 14, 2019

An updated definition of chronic liver disease that captures cirrhosis-related deaths would help correct the current underestimation of mortality rates reported by the Centers for Disease Control and Prevention (CDC), report researchers.

"The CDC definition of chronic liver disease is very narrow," said Connor Griffin, MD, from the Baylor University Medical Center in Dallas. Currently, it only encompasses three International Classification of Diseases (ICD) 10 codes: K70, for alcoholic liver disease; K73, for chronic hepatitis; and K74, for fibrosis and cirrhosis.

An updated definition — with a "more comprehensive" list that adds codes for hepatocellular carcinoma and complications of cirrhosis — has been shown to have a 93% positive predictive value for identifying cirrhosis and a 98% positive predictive value for identifying cirrhosis-related complications, Griffin told Medscape Medical News.

For their study, he and his colleagues assessed whether the update would capture more cirrhosis-related deaths than the CDC definition. They used mortality data from the CDC National Death Index collected over nearly 2 decades — 1999 to 2017 — and compared age-adjusted mortality rates for the two definitions.

In line with previous findings, the CDC definition underestimated mortality, capturing only 65% of deaths related to chronic liver disease in 2017, Griffin reported at the Liver Meeting in Boston. However, with the updated definition, there was a 47% increase in the age-adjusted mortality rate.

In fact, the update captured more deaths than the CDC definition for all race, sex, and age subgroups.

In 2017, the CDC definition captured 71% of deaths related to chronic liver disease in the white population, but only 66% in the Hispanic population, 50% in the black population, and 28% in the Asian population, suggesting racial disparity.

"If the data in this abstract are true, we are disadvantaging minority populations with liver disease by not capturing them well in our estimates," Ponni Perumalswami, MD, associate professor at the Icahn School of Medicine at Mount Sinai in New York City, told Medscape Medical News.

Disparity by sex was also seen with the CDC definition. From 2008 to 2017, the mortality rate for men ticked up while the rate for women remained largely unchanged.

For age, the difference in mortality rates between the two definitions was greater for the population older than 65 years than younger than 65, indicating that the CDC underestimation might be more pronounced in older populations.

"A False Sense of Reassurance"

The concern with underestimation is that it gives "a false sense of reassurance" that the burden of liver disease is low, Griffin explained. "We believe that by using a more comprehensive and accurate definition, both researchers and policy makers will be able to notice trends in liver-related mortality not captured by the CDC and act appropriately, especially in the older Medicare-eligible population."

One limitation of the study is that it focused "exclusively" on cirrhosis and its related complications, and "likely still under-represents the CLD burden," Griffin acknowledged, noting that other common causes of chronic liver disease mortality, such as sepsis and renal disease, were not captured.

Another limitation is that the data are "vulnerable" to misclassification bias because they were obtained from death certificates, he added. "However, this bias should be present in both definition groups and over the entire study course," and should affect both the CDC and updated numbers equally.

When asked whether the updated definition could overestimate mortality, Griffin said it would be "unlikely," given the positive predictive values for the update — 93% for cirrhosis and 98% for cirrhosis-related complications — and given that all codes evaluated for complications of cirrhosis are "strongly" associated with cirrhosis.

"If anything, the updated definition may still underestimate CLD-related mortality, given that death certificate misclassification bias tends to favor cardiopulmonary arrest, which was captured by this study," Griffin added.

The Liver Meeting 2019: American Association for the Study of Liver Diseases (AASLD): Abstract 0122. Presented November 10, 2019.

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