The number of fatal opioid overdoses may have been higher than previously reported, with some states greatly underestimating the effect of opioid-related deaths, an analysis of National Center for Health Statistics data suggests.

Potentially 70,000 opioid-related overdose deaths from 1999 to 2015 were not included in national figures because coroners and medical examiners did not specify the drugs contributing to death, reported Jeanine Buchanich, PhD, of the University of Pittsburgh, and coauthors in Public Health Reports.

“Our new research tells us that several states are likely dramatically underestimating the effect of opioid-related deaths because of incomplete drug reporting on death certificates,” Buchanich told MedPage Today.

“Incomplete death certificate reporting hampers the efforts of lawmakers, treatment specialists, and public health officials,” she added. “The large differences we found between states in the completeness of opioid-related overdose mortality reporting make it more difficult to identify geographic regions most at risk.”

The analysis supports other recent research that suggests that death certificate reports understate the prevalence of opioid, heroin, and synthetic opioid-involved mortality in the United States.

Drug-specific overdose deaths are identified by ICD-10 T codes, which are assigned by the coroner or medical examiner completing the death certificate. A code of T50.9 indicates poisoning by “other and unspecified drugs, medicaments, and biological substances.”

In this study, Buchanich and colleagues abstracted unintentional drug overdose deaths with contributory T codes (T36.0-T50.9) from the Mortality Multiple Cause Data Files of the National Center for Health Statistics from 1999 to 2015. The team reallocated unspecified overdose deaths for each state and year, assuming that their proportion would be the same as the proportion of opioid-related deaths among all fatal overdoses.

In five states — Alabama, Indiana, Louisiana, Mississippi, and Pennsylvania — more than 35% of overdose death certificates didn’t name a drug. Reallocation reclassified more than 70,000 unspecified fatal overdoses to opioid-related deaths, ranging from nine in Vermont to 11,152 in Pennsylvania.

“Generally, this study provides additional confirmatory evidence that opioid and other sources of drug deaths will be undercounted when not accounting for the T50.9 unspecified drug category,” observed health economist Christopher Ruhm, PhD, of the University of Virginia, who was not involved in the analysis. “It makes the point that better reporting of the sources of drug deaths is needed.”

Part of the problem may stem from the coroner system in each state, Buchanich noted. In most states, elected coroners are not required to be physicians.

“States with a decentralized county coroner system, or those with a hybrid system that involved county coroners and medical examiners, were likely to have a higher proportion of overdose deaths with unspecified drug codes,” she said.

But over the 17-year period, several states made extensive efforts to improve reporting.

“In Kentucky, for example, opioid-related drug codes increased 43% from 1999 through 2015, and unspecified drug reporting decreased 28%,” Buchanich noted. “This suggests that state-based efforts can be instrumental in improving the accuracy of drug-specific reporting for overdose deaths.”