We used cross-sectional data from the 1999–2004 National Health and Nutrition Examination Survey (NHANES), a national population-based health survey that includes personal interviews, medical examinations, and laboratory measurements (21).

These analyses were based on data from adults aged 18–64 years who had fasted for ≥8 h. Individuals aged >64 years were excluded because they were commonly entitled to Medicare, the federal health care insurance program (96 of 1,988 subjects aged ≥65 years had undiagnosed diabetes, of whom only 2 reported no health care insurance coverage). The diabetic population consisted of subjects who answered “yes” to the question, “Have you ever been told by a doctor that you have diabetes or sugar diabetes?” plus subjects who answered “no” but had fasting plasma glucose levels ≥126 mg/dl. Those who answered “no” (regardless of fasting plasma glucose values) made up our population who self-reported not having diabetes.

Access to health care can be considered a multidimensional concept, including availability, organization, financing, utilization, and satisfaction among the possible domains (7). In this study, the measures of access used reflect two of these five domains: financing and utilization (7). Financing was measured by the following three variables: 1) uninsured, 2) covered by private insurance, and 3) continuity of insurance coverage. Classified as uninsured were those who responded “no” to the question, “Are you covered by health insurance or some other kind of health care plan?” Those who reported having health insurance (the insured) were asked, “Are you covered by private insurance?” Those who responded “yes” were classified as covered by private insurance, and those responding “no” were considered to have public insurance. Continuity of coverage was derived from three questions: “Are you covered by health insurance or some other kind of health care plan?”, “In the past 12 months, was there any time when you did not have any health insurance coverage?”, and “About how long has it been since you last had healthcare coverage?” The responses were used to create a three-level variable: continuously insured over the past year, uninsured ≤1 year, and uninsured >1 year.

Utilization was measured by 1) number of times the participant received health care during the past 12 months, derived from the question, “During the past 12 months, how many times have you seen a doctor or other healthcare professional about your health at a doctor's office, a clinic, hospital emergency room, at home or some other place?” and 2) routine patterns of health care utilization, derived from the two questions, “Is there a place that you usually go when you are sick or you need advice about your health?” and “What kind of place do you go to most often: is it a clinic, a doctor's office, ER, or some other place?”

We controlled for six sociodemographic variables in our analysis, including age, sex, race/ethnicity, marital status, education, and family income. We also used as covariates BMI (measured as kilograms divided by the square of height in meters) and a dichotomized version of self-rated health.

In the subsample of adults aged 18–64 years who had fasted, we identified 110 subjects with undiagnosed diabetes, 704 who had been diagnosed, and 4,782 subjects without diabetes. Characteristics of participants for each group was presented in Table 1.

In an analysis adjusted for age, sex, and race/ethnicity, those with undiagnosed diabetes had the least favorable profile of access to health care among the three groups (Table 2 ). They were significantly more likely to be uninsured than either of the other two groups (P < 0.01 for both comparisons). Similarly, they were more likely to be uninsured for >1 year than were these other two groups (P < 0.01), and they were the most likely not to have received any health care in the past year. In addition, subjects with undiagnosed diabetes were more likely than those with diagnosed diabetes to lack a usual source of care (P < 0.01). If insured, however, the undiagnosed were more likely than the diagnosed to be covered by a private insurance plan.

Having undetected diabetes puts one's health at substantial risk (1,2), but timely detection of diabetes is difficult without access to health care. Using a nationally representative sample, we found that lack of access to care significantly elevated the risk of going undiagnosed. We found that undetected diabetes was related to insurance coverage, routine patterns of health care utilization, and continuity of coverage. The type of insurance and the number of times a health care professional was seen in the past year were also associated with having undetected diabetes. It is also noteworthy that those with undiagnosed diabetes were significantly more likely than those without diabetes to be uninsured or to be uninsured for >1 year.

Previous studies (9–11) have indicated that continuity of coverage is even more important than coverage per se in determining health status. Similarly, our study indicated that access to care was significantly related to the failure to detect diabetes, and the continuity of access was also important in determining whether diabetes would go undetected. In our study, subjects uninsured for >1 year were essentially twice as likely as insured subjects without a break in insurance over the past year to have undetected diabetes. Type 2 diabetes, a chronic disease, takes a long time to develop and reach its diagnostic threshold. During the progression to diabetes, access to primary care plays a crucial role in its timely detection. The longer an individual is without insurance coverage, the longer she or he may go with undetected diabetes.

We found that those covered by private plans were significantly more likely to be undiagnosed when they actually had diabetes than were those covered by government insurance. This finding may seem counterintuitive, but we know that some private insurance companies provide limited coverage for preventive care (17,23), and private coverage tends to be more discontinuous (24). It is worth noting that some government health plans (e.g., those offered through the Department of Veterans Affairs) provide relatively effective preventive care for their enrollees with diabetes (17), and the Veteran's Affairs professional staff may accordingly be more attuned to recommendations for diabetes screening.

Previous studies (19,20) have not found a relationship between education or income and the risk of having undetected diabetes. These studies, however, did not examine the role played by access to health care (another aspect of socioeconomic status) in the detection of diabetes. Although we found no significant difference by education or income between being diagnosed and undiagnosed among individuals with diabetes, our analyses have shown that access to health care plays an important role in detecting diabetes.

Although race/ethnicity is related to diabetes and poor access to care (1,25), we found no evidence that race/ethnicity affects the association between access to health care and detection of diabetes. A recent study (26), using data from Behavioral Risk Factor Surveillance System 1998–2001, found that individuals of lower socioeconomic status were at greater risk for not receiving preventive care regardless of race/ethnicity and those without health insurance coverage were at the greatest risk for not receiving preventive services. Our findings are consistent with that study. In our model, lack of access to health care is a predictor for undetected diabetes regardless of race/ethnicity. Our study suggests that access to health care might be among the most important predictors for determining whether diabetes is/is not detected.

Our study has the following strengths: 1) The data come from a nationwide survey; 2) sampling weights were incorporated in the analysis so as to represent the adult U.S. population; 3) sociodemographic, anthropometric, and health status variables were controlled for in our analyses; and 4) two different approaches were used to examine two different populations, reducing the bias introduced by the effect of diabetes awareness on the willingness to acquire health care insurance. Our study has limitations as well. The major limitation is that the relatively small sample of subjects with undiagnosed diabetes makes it difficult to analyze differences by subgroup between the two sexes or between different race/ethnicity groups. Another limitation is that access to health care was measured by only two of five domains because of the limited availability of the survey data.

Our findings demonstrate that lack of access to health care may result in missed opportunities to detect diabetes. The detection of diabetes requires specific diagnostic tests, e.g., the fasting plasma glucose test or the oral glucose tolerance test (or both). These tests are commonly arranged within a comprehensive health care setting that recognizes the risk profiles of its patients. Without access to comprehensive health care, patients would be less likely to receive screening and diagnostic services, and, in the end, their diabetes may be missed by the health care system. When they are missed by the health care system, the problems caused by those “missed” cases do not disappear. On the contrary, as a study by Young and Mustard (27) indicated, they represent the unseen but clinically important burden of diabetes, with significant concurrent metabolic derangements and a long-term impact on use of health care.

With the increases in both the diabetic and the uninsured populations in the U.S., it seems very likely that the number of undetected cases of diabetes will increase in the future, with consequent increases in diabetes-related morbidity and mortality. This trend cannot be reversed until we can increase access to health care for those Americans who need it most. Our analyses indicate that limited health care access, especially being uninsured and having a long period without insurance, is associated with being a “missed patient” with diabetes. Those making an effort to increase the timely detection of diabetes should consider issues related to health care access.