Responses to a payment policy denying professional charges for diagnostic imaging by nonradiologist physicians.

OBJECTIVE: To assess the impact of a payment policy denying reimbursement for the imaging-related professional services of nonradiologist physicians by comparing the use of and expenditures for diagnostic imaging examinations before and after implementation of the policy. DESIGN: Retrospective economic evaluation of claims and expenditures for diagnostic imaging examinations filed by physicians practicing in the 20 US counties having the greatest number of United Mine Workers of America Health and Retirement Funds (hereafter referred to as Funds) beneficiaries. SETTING: Insurance claims database of Funds beneficiaries, most of whom are elderly and live in rural communities and small towns. INTERVENTION: The January 1, 1993, implementation of a reimbursement policy denying payment of professional claims for diagnostic imaging of nonradiologist physicians. MAIN OUTCOME MEASURES: Numbers and types of eligible claims and Funds payments for diagnostic imaging examinations during the year before and after the intervention, normalized for changes in the number of beneficiaries. RESULTS: Despite the rejection of $811,466 in claims disallowed by the policy, the Funds paid 12% more for diagnostic imaging performed in the 20 counties we studied during 1993 than during 1992. The Funds reimbursed 41% more claims per beneficiary for diagnostic imaging in 1993 than in 1992 (t = -8.03, P < .0001). The absolute number of professional claims per beneficiary increased more than did technical or global claims. CONCLUSIONS: Despite a payment policy designed, in part, to reduce the Funds' imaging-related expenditures, the physicians we studied filed more claims, leading to greater expenditures. An increased number of self-referred technical claims and greater referral to hospital radiology departments likely account for most of the observed increases in utilization and costs.

Time-dependent inhibition of gamma-aminobutyric acid aminotransferase, by 3-hydroxybenzylhydrazine.

gamma-Aminobutyric acid (GABA) aminotransferase is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the conversion of GABA into succinic semialdehyde. Hydrazine analogues have long been known to act as inactivators of PLP-dependent enzymes, including GABA aminotransferase, however, no studies of the molecular mechanism of inactivation of PLP-dependent enzymes by hydrazines have been reported. 3-Hydroxybenzylhydrazine is shown to be a potent in vitro time-dependent inhibitor of pig brain GABA aminotransferase. UV-visible and 1H NMR studies, both with GABA aminotransferase and with PLP as a chemical model for the enzyme-catalyzed reaction, indicate that 3-hydroxybenzylhydrazine reacts both enzymatically and nonenzymatically to form the 3-hydroxybenzylhydrazone of PLP without tautomerization.

Inactivation of gamma-aminobutyric acid aminotransferase by L-3-chloroalanine hydroxamate.

The mechanism of inactivation of gamma-aminobutyric acid aminotransferase (GABA-AT) by L-3-chloroalanine hydroxamate (1) was investigated. Inactivation of [3H]PLP-reconstituted GABA-AT with 1 followed by denaturation gave no PMP or enamine adduct to the PLP; however, a new unknown metabolite was observed which was identical to the metabolite formed upon inactivation of GABA-AT by L-cycloserine. Time-dependent inactivation occurs, but the kinetics are second order; the rate of inactivation increases with time. After inactivation occurs the addition of fresh enzyme results in a faster rate of inactivation than prior to the initial inactivation. This indicates that the actual inactivator is generated from L-3-chloroalanine hydroxamate, and is not L-3-chloroalanine hydroxamate itself. Added gabaculine-inactivated enzyme to fresh enzyme does not increase the rate of inactivation, suggesting that the conversion of L-3-chloroalanine hydroxamate to the active form is not catalyzed by peripheral amino acid residues. L-3-Chloroalanine hydroxamate was shown to undergo buffer-catalyzed cyclization to L-cycloserine, which is the actual inactivator of GABA-AT.

Physicians' utilization and charges for outpatient diagnostic imaging in a Medicare population.

OBJECTIVES AND RATIONALE: For 10 common clinical presentations, we assessed differences in physicians' utilization of and charges for diagnostic imaging, depending on whether they performed imaging examinations in their offices (self-referral) or referred their patients to radiologists (radiologist-referral). METHODS: Using previously developed methodologies, we generated episodes of medical care from an insurance claims database. Within each episode, we determined whether diagnostic imaging had been performed, and if so, whether by a self-referring physician or a radiologist. For each of the 10 clinical presentations, we compared the mean imaging frequency, mean imaging charges per episode of care, and mean imaging charges for diagnostic imaging attributable to self- and radiologist-referral. RESULTS: Depending on the clinical presentation, self-referral resulted in 1.7 to 7.7 times more frequent performance of imaging examinations than radiologist-referral (P < .01, all presentations). Within all physician specialties, self-referral uniformly led to significantly greater utilization of diagnostic imaging than radiologist-referral. Mean imaging charges per episode of medical care (calculated as the product of the frequency of utilization and mean imaging charges) were 1.6 to 6.2 times greater for self-referral than for radiologist-referral (P < .01, all presentations). When imaging examinations were performed--including those performed in both physicians' offices and hospital outpatient departments--mean imaging charges were significantly greater for radiologists than for self-referring physicians in seven of the clinical presentations (P < .01). This result is related to the high technical charges of hospital outpatient departments; in office practice, radiologists' mean charges for imaging examinations were significantly less than those of self-referring physicians for seven clinical presentations (P < .01). CONCLUSIONS: Nonradiologist physicians who operate diagnostic imaging equipment in their offices perform imaging examinations more frequently, resulting in higher imaging charges per episode of medical care. These results extend our previous research on this subject by their focus on a broader range of clinical presentations; a mostly elderly, retired population; and the inclusion of higher-technology imaging examinations.