The number of Independent Medical Review decision letters issued in response to California workers’ compensation medical disputes is trending up in the last few years after declining steadily from 2018 through 2022, a report out on Thursday shows.
IMR decision letters started increasing in 2023, 2024 and through the first quarter of 2025, according to the California Workers’ Compensation Institute.
However, the uphold rate for medical service modifications and denials remains close to 90%, according to CWCI.
CWCI’s latest review of IMR activity and outcomes examined 1.57 million IMR decision letters issued from 2015 through March in response to applications submitted to the state after a Utilization Review physician modified or denied a workers’ comp medical service request.
CWCI tracked the number of letters issued quarterly, determined the distribution and uphold rates for disputed treatment requests by type of medical service, measured IMR response times and calculated the percentage of IMRs associated with high-volume physicians.
IMR was introduced in 2013 as part of a sweeping workers’ comp reform in California. It was expected to reduce medical disputes by helping to ensure that workers’ comp treatment met evidence-based medicine standards.
However, the CWCI said it wasn’t until 2019 that the number of IMR disputes began a steady decline: the number of IMR decision letters fell by 31% from a peak level of 184,385 in 2018 to 127,215 in 2022. The decline coincided with a reduction in the number of job injury claims during the pandemic and a drop in the number of pharmaceutical disputes after the state added Pain Management and Opioid Guidelines to its Medical Treatment Utilization Schedule (MTUS) in late 2017 and adopted the MTUS Drug Formulary in January 2018.
According to the CWCI, more recent data show IMR letter volume rose 2.9% in 2023 and 8.2% in 2024, and initial results for this year show the trend accelerating (there were 38,393 IMR decision letters in the first three months of 2025).
Disputes over prescription drug requests represented 30.6% of all IMRs in the first quarter, which was more than any other type of medical service, but that was down from 33.4% in 2024 and 50.7% in 2015. Much of that decline was due to the reduction in IMRs involving opioid requests, which fell from 32% of all pharmaceutical IMRs in 2018 to 18.6% in the first quarter of this year, according to CWCI.
A small number of physicians drove much of the IMR activity: the top 1% of requesting physicians (81 doctors) accounted for 42.2% of the disputed service requests that underwent IMR in the 12 months ending on March 30, and the top 10 individual physicians accounted for 10.9% of the disputed requests, according to CWCI.
CWCI members and subscribers can obtain a detailed summary of IMR experience through March 2025 in Bulletin 25-09 on the institute’s website.
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