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A new California Workers’ Compensation Institute (CWCI) review of the Independent Medical Review (IMR) process shows that after hitting an all-time low high in 2022, the number of IMR decision letters rose 4.1% in the first six months of 2023 compared to the first half of 2022. However the number of letters and individual decisions remained below pre-pandemic levels.

CWCI’s review encompassed more than 1.3 million IMR decision letters issued from 2015 through June 2023 in response to applications submitted to the state after a Utilization Review (UR) physician modified or denied a workers’ comp medical service request.

As in prior reviews, Institute analysts tallied the number of letters issued each quarter based on the letter date; determined the distribution and uphold rates by medical service category for the disputed treatment requests, as well as the distribution and outcomes of pharmaceutical IMRs by major therapeutic drug group; and calculated the percentage of IMRs associated with high-volume medical providers.

The data show that total IMR volume trended down for four consecutive years (2019 through 2022), as the number of work injury claims fell during the pandemic and pharmaceutical disputes declined after the state adopted the evidence-based Medical Treatment Utilization Schedule (MTUS) Prescription Drug Formulary and Pain Management and Opioid Guidelines.

After climbing to a record 184,735 letters in 2018, IMR letter volume declined 31.1% over the next four years, falling to 127,215 letters in 2022. While IMR decisions were down across all medical service categories, the addition of the Pain Management and Opioid Guidelines into the MTUS in late 2017 and the implementation of the MTUS Formulary in January 2018 had a huge effect as prescription drug disputes fell from 47.3% of all IMRs in 2017 to 33.3% in 2022, while the initial data from 2023 show prescription drug disputes fell to 32.6% of the IMRs in of the first half of this year.

From 2018 through June of this year, opioids’ share of the pharmaceutical IMRs has dropped from nearly a third to less than a quarter of all prescription drug IMRs. With prescription drugs representing a smaller share of the IMR disputes, there has been a shift in the distribution of services submitted for IMR since 2018, with the biggest percentage increases noted in physical therapy, which jumped from 10.3% to 13.4% of the IMRs; injections, which increased from 9.0% to 12.1%; and durable medical equipment, prosthetics, orthotics and supplies (DMEPOS), which rose from 7.1% to 8.9% of the IMRs over the past 5-1/2 years.

As in previous reviews, the latest data show that a small number of physicians continue to drive much of the IMR activity, with the top 1% of requesting physicians (80 doctors) accounting for 40.3% of the disputed service requests that underwent IMR in the 12 months ending on June 30 of this year. The top 10 individual physicians alone accounted for 11.6% of the disputed requests, and notably, 9 of the 10 individual providers with the highest number of IMR requests a year earlier were still on the top 10 list in the latest review.

IMR outcomes remained fairly stable, with IMR physicians upholding UR doctors’ modifications or denials 89.2% of the time in the first half of 2023 versus 91.1% of the time in 2022. The 2023 uphold rates by type of service request ranged from 75.7% for evaluation/management services to 92.9% for acupuncture.

CWCI members and subscribers will find a more detailed summary of IMR experience through June 2023 in Bulletin 23-11 at, and Institute members can also access updated IMR slides under the Research tab.