We examined hospitals that exclusively used the billing modifier QZ in anesthesia claims for a 5% sample of Medicare beneficiaries in 2013. We used a national Medicare provider file to identify physician anesthesiologists and nurse anesthetists affiliated with these hospitals. Among the 538 hospitals that exclusively reported the modifier QZ, 47.5% had affiliated physician anesthesiologists. These hospitals accounted for 60.4% of the cases. Our results illustrate the challenges of using modifier QZ to describe anesthesia practice arrangements in hospitals. The modifier QZ does not seem to be a valid surrogate for no anesthesiologist being involved in the care provided.
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