Research Design and Methods
Quest Diagnostics maintains the largest private clinical laboratory database in the U.S. Consisting of deidentified data on nearly 2 billion patient encounters since 2000, the database provides laboratory information on the vast majority of conditions and diseases affecting the U.S. population. Quest Diagnostics has approximately 150 million patient encounters annually with individuals from all states and the District of Columbia. The overall testing volume declined slightly in the study period (first half of 2014) compared with the control period (first half of 2013). This Quest Diagnostics Health Trends study was determined to be exempt by the Western Institutional Review Board.
The Quest Diagnostics database was queried for patients 19–64 years of age meeting our laboratory criteria for newly identified diabetes in the pre-Medicaid expansion control period (January–June 2013) or the postexpansion study period (January–June 2014). Newly identified diabetes was defined as having an ICD-9 diagnosis code of 250.x (diabetes) or a hemoglobin A1c of >6.4% (46 mmol/mol) within the control or study period and the absence of both in the preceding calendar year (January–December 2012 for control period and January–December 2013 for the study period). Importantly, all patients included in this analysis had to have had at least one test through Quest Diagnostics in the preceding calendar year. This was to assure that we identified patients with only newly identified diabetes on the premise that patients with diabetes should receive hemoglobin A1c testing and are likely to have been assigned an ICD-9 code of diabetes in the preceding year.
Patients were categorized as being Medicaid enrollees if they were enrolled in Medicaid at the time diabetes was diagnosed having a hemoglobin A1c >6.4% (46 mmol/mol) or an ICD-9 code of 250.x (diabetes) in the control period or study period. Medicaid, including managed Medicaid, was listed on the test requisition as one of the payers.
The residence (state or District of Columbia) of each patient was based on the address provided for the patient at the time of testing that was used for categorization of the patient as having newly identified diabetes.
Hemoglobin A1c testing was performed using the Roche Cobas Integra (Indianapolis, IN), which is National Glycohemoglobin Standardization Program certified. Statistical significance of comparisons was tested using Pearson χ2 test to assess the difference between proportions. Analyses were performed in SAS 9.4 (SAS Institute, Inc., Cary, NC).
Diabetes Care. 2015;38(5):833-837. © 2015 American Diabetes Association, Inc.
