In this study of patients without known diabetes, the majority (78%) had 1 or more glucose tests ordered over a 3-year period. One in seven glucose values (14%) was potentially abnormal. When the glucose value was 110 mg/dl or greater, physicians interpreted these as normal 16% of the time and did not indicate plans for any subsequent work-up 50% of the time.
Although glucose testing does not always represent intentional screening, the patterns of testing were not random. Selected risk factors for diabetes (age 45 years and older, non-white ethnicity and family history of diabetes) independently increased the odds of glucose testing. Hypertension and hyperlipidemia were not associated with glucose testing, even though chemistry panels that include glucose are often ordered to monitor these diseases. These findings suggest that intentional screening for diabetes is occurring, even if physicians are not documenting this reason for glucose testing.
Glucose testing most closely resembled the guidelines of the ADA, based on the high rate of testing for eligible patients (97%) and the strong association of ADA-specific selection factors (such as non-white ethnicity and family history) with glucose testing. However, "adherence" to the CDC and USPSTF guidelines were also high, indicating that many of the risk factors used to select patients for screening are correlated with each other (age with hypertension, for example).
Our study builds on the findings of previous research. Ealovega and colleagues found that 69% of primary care patients received glucose testing over a 3-year period in a managed care setting [8
], which is consistent with our finding of 78%. Ealovega and colleagues also found that only 38% of abnormal results received appropriate follow-up, consistent with our finding of 50% [8
]. Other investigators found that glucose testing was associated with age [5
] and family history of diabetes [6
]. However, several of these previous analyses were limited by incomplete adjustment for potential confounders [5
]. Ours was the only study to find an independent effect of ethnicity on the odds of glucose testing. Our finding that hypertension and hyperlipidemia were not independent predictors of glucose testing is in contrast to others' [8
]. None of the previous studies specifically compared practice patterns to national screening guidelines.
Failure to recognize abnormal glucose values represents a missed opportunity to identify and treat incident diabetes or pre-diabetes, with timely treatment of pre-diabetes having the potential to prevent or delay the onset of diabetes [16
]. That follow-up rates were higher for patients who had all visits with the same primary care physician is intriguing but based on a relatively small sample size and warrants replication in larger studies. There are several reasons why physicians may not act upon abnormal values: they may not have seen the values, may not have recognized their importance, or may have been giving their attention to competing demands. Indeed, a study that surveyed physicians about test result management in general found that only 52% of respondents reported keeping a record of tests that they had ordered and 83% acknowledged delays in recognizing and acting upon abnormal results, saying that they had reviewed at least 1 test result in the last 2 months that they "wished they had seen earlier" [17
This study had several strengths. We used electronic orders for actual glucose tests, rather than patients' self-report of testing. We included an ethnically diverse patient population, with a proportion of ethnic minorities (41%) similar to that in the U.S. overall (37%) [18
]. We followed patients over time, allowing for multiple primary care visits and approximating the 3-year screening interval suggested by the ADA. In addition, we used the rigorous statistical method of multiple imputation to account for missing data.
Several limitations merit discussion. First, height was missing for a substantial proportion of patients; however, results were similar when the multivariate model was performed with and without this variable. Second, we did not have enough power to adjust for clustering by physician, making it possible that some physicians' practice styles weighted the results more heavily than others'. Third, the study took place in one institution that may not be generalizable to other settings. Fourth, this study may actually underestimate the proportion of abnormal glucose values, because glucose values may be falsely low if the samples are not processed promptly. Fifth, patients who came for initial visits in 1999 may vary from patients who came only for subsequent visits that year. Sixth, it is possible that some patients with known diabetes did not report their condition at the initial visit, although this is unlikely because only 1 patient was diagnosed with diabetes – based on an abnormal glucose – after the initial visit; most patients diagnosed with diabetes were diagnosed after subsequent visits. Finally, as in all studies that examine medical records, some results were dependent on what physicians documented, although we minimized this by including in the analysis any glucose test ordered rather than only glucose tests for which screening was documented as the purpose.