Along with requirements for personnel qualifications and quality control testing, proficiency testing (PT) is one of the central safeguards of laboratory quality under the Clinical Laboratory Improvement Amendments of 1988 (CLIA)1 and its regulations.2 The CLIA regulations have often been compared to a three-legged stool, resting on requirements for personnel qualifications and two performance indicators: quality control testing and proficiency testing. Proficiency testing is the only external performance indicator required by CLIA.

CONTEXT: Changes in reimbursements for clinical laboratory testing may help us assess the effect of various variables, such as testing recommendations, market forces, changes in testing technology, and changes in clinical or laboratory practices, and provide information that can influence health care and public health policy decisions. To date, however, there has been no report, to our knowledge, of longitudinal trends in national laboratory test use. OBJECTIVE: To evaluate Medicare Part B-reimbursed volumes of selected laboratory tests per 10,000 enrollees from 2000 through 2010. DESIGN: Laboratory test reimbursement volumes per 10,000 enrollees in Medicare Part B were obtained from the Centers for Medicare & Medicaid Services (Baltimore, Maryland). The ratio of the most recent (2010) reimbursed test volume per 10,000 Medicare enrollees, divided by the oldest data (usually 2000) during this decade, called the volume ratio, was used to measure trends in test reimbursement. Laboratory tests with a reimbursement claim frequency of at least 10 per 10,000 Medicare enrollees in 2010 were selected, provided there was more than a 50% change in test reimbursement volume during the 2000-2010 decade. We combined the reimbursed test volumes for the few tests that were listed under more than one code in the Current Procedural Terminology (American Medical Association, Chicago, Illinois). A 2-sided Poisson regression, adjusted for potential overdispersion, was used to determine P values for the trend; trends were considered significant at P < .05. RESULTS: Tests with the greatest decrease in reimbursement volumes were electrolytes, digoxin, carbamazepine, phenytoin, and lithium, with volume ratios ranging from 0.27 to 0.64 (P < .001). Tests with the greatest increase in reimbursement volumes were meprobamate, opiates, methadone, phencyclidine, amphetamines, cocaine, and vitamin D, with volume ratios ranging from 83 to 1510 (P < .001). CONCLUSIONS: Although reimbursement volumes increased for most of the selected tests, other tests exhibited statistically significant downward trends in annual reimbursement volumes. The observed changes in reimbursement volumes may be explained by disease prevalence and severity, patterns of drug use, clinical or laboratory practices, and testing recommendations and guidelines, among others. These data may be useful to policy makers, health systems researchers, laboratory directors, and industry scientists to understand, address, and anticipate trends in laboratory testing in the Medicare population.