Abstract
This cross-sectional study uses NHANES survey data to examine trends in glycemic control and patient awareness of HbA1c test results and targets between 2007 and 2014.
In 2014, an estimated 30.3 million people (9.4%) in the United States had diabetes. Improving glycemic control reduces the risk of diabetes-related vascular complications. Studies have shown improvement in glycemic control in the United States from 1998 through 2010, as measured by hemoglobin A1c (HbA1c). We examined recent trends in glycemic control and patient awareness of HbA1c test results and targets.
Methods
The study was exempted from review by the institutional review board at Tufts Medical Center. We used data from 4 survey periods of the National Health and Nutrition Examination Survey (NHANES; survey periods: 2007-2008, 2009-2010, 2011-2012, and 2013-2014), a representative sample of the US noninstitutionalized population with average response rates of 75.4% for the study period. A subsample of surveyed participants was asked to complete laboratory tests and physical examinations. Respondents 20 years and older who reported having diabetes diagnosed by a clinician were included in this analysis.
We calculated the proportion of survey participants with an HbA1c level less than 7% (good control), less than 8% (moderate control), and greater than 9% (poor control). We also calculated the proportion of participants who reported having a test for HbA1c in the prior year and who were aware of their HbA1c result and their target HbA1c level. We analyzed results by subgroups of age (20-44, 45-65, and >65 years), race (white vs nonwhite), and sex. Survey weights were used to calculate proportions. P values for trend over the 4 survey periods were calculated using a multilevel logistic regression in STATA (StataCorp), version 14. Age, sex, body mass index, race, insurance status, education, and income were included as covariates of the first level, and survey period as the dependent variable of the second level. No covariates were included for the subgroup trend analyses. Significance was defined as a 2-tailed P value less than .05.
Results
Of 23 482 participants, 2908 (12.40%) reported having diabetes (mean age, 62 years [SD, 12.96]; women, 50.40%; white race, 35.80% [unweighted]). Median HbA1c level was 6.90% (interquartile range [IQR], 6.20%-8.15%) in 2007-2008 and 6.95% (IQR, 6.30%-8.20%) in 2013-2014 (P = .39) (Table 1). Glycemic control did not change between 2007-2008 and 2013-2014 overall or in any subgroup (Table 1). Over time, a higher proportion of patients with diabetes reported having an HbA1c test within the past year; 55.10% (95% CI, 49.69%-60.50%) in 2007-2008 to 77.78% (95% CI, 75.07%-80.48%) in 2013-2014 (P value for trend <.001) (Table 2). All subgroups showed a similar change. In 2007-2008, 52.32% (95% CI, 47.63%-57.00%) of patients reported being aware of their past year HbA1c result. This proportion increased to 74.31% (95% CI, 69.63%-78.99%) in the 2013-2014 survey (P value for trend <.001). The change was statistically significant in all subgroups except participants aged 20 to 44 years (P value for trend = .16). The proportion of participants who were aware of the target HbA1c level set by their clinician increased from 2007-2008 (74.07% [95% CI, 70.48%-77.66%]) to 2013-2014 (89.70% [95% CI, 86.11%-93.29%]) (P value for trend <.001). The change was statistically significant in all subgroups except participants aged 20 to 44 years (P value for trend = .81) (Table 2).
Table 1. Hemoglobin A1c (HbA1c) Levels in Participants Reported as Having Diabetes (NHANES 2007-2008 Through 2013-2014)a.
| Participants, Weighted % (95% CI) by NHANES Period | P Value for Trend | ||||
|---|---|---|---|---|---|
| 2007-2008 (n = 757) |
2009-2010 (n = 725) |
2011-2012 (n = 704) |
2013-2014 (n = 722) |
||
| HbA1c level, median (IQR), % | 6.90 (6.20-8.15) | 6.90 (6.20-7.80) | 6.90 (6.30-6.80) | 6.95 (6.30-8.20) | .39 |
| With HbA1c >9% (poor glycemic control) | |||||
| Overall | 13.68 (11.50-15.85) | 11.31 (8.74-13.87) | 16.1 (12.37-19.82) | 14.98 (11.78-18.17) | .99 |
| Age range, y | |||||
| 20-44 | 22 (9.96-34.03) | 27.46 (14.36-40.55) | 32.34 (15.81-48.86) | 19.76 (9.02-30.50) | .56 |
| 45-65 | 15.92 (12.74-19.09) | 12.24 (9.67-14.80) | 16.21 (12.13-20.28) | 19.11 (15.24-22.97) | .91 |
| >65 | 8.18 (5.26-11.10) | 5.51 (3.24-7.78) | 10.49 (6.550-14.42) | 8.00 (4.40-11.61) | .63 |
| Raceb | |||||
| White | 12.14 (9.20-15.07) | 6.66 (4.74-8.58) | 12.02 (7.79-16.25) | 11.94 (7.88-15.99) | .17 |
| Nonwhite | 16.53 (13.41-19.64) | 18.3 (14.10-22.49) | 22.03 (17.71-26.34) | 20.27 (16.27-24.26) | .71 |
| Sex | |||||
| Men | 14.38 (9.58-19.18) | 13.71 (9.97-17.45) | 15.86 (9.69-22.03) | 15.08 (10.90-19.25) | .95 |
| Women | 13.04 (10.45-15.62) | 8.78 (5.39-12.17) | 16.35 (11.48-21.21) | 14.88 (9.7-19.99) | .28 |
| With HbA1c <8% (moderate glycemic control) | |||||
| Overall | 77.27 (73.38-81.15) | 81.05 (76.54-85.55) | 71.14 (65.78-76.49) | 73.32 (69.53-77.10) | .47 |
| Age range, y | |||||
| 20-44 | 64.23 (49.94-78.51) | 61.09 (46.35-75.82) | 56.09 (38.64-73.53) | 72.48 (62.36-82.59) | .39 |
| 45-65 | 74.05 (68.62-79.47) | 80.74 (74.62-86.85) | 65.78 (57.37-74.18) | 68.03 (62.48-73.57) | .16 |
| >65 | 85.5 (81.79-89.20) | 87.33 (83.76-90.89) | 82.73 (76.88-88.57) | 80.33 (74.58-86.07) | .67 |
| Raceb | |||||
| White | 79.1 (74.65-83.54) | 84.88 (79.21-90.54) | 74.1 (66.45-81.74) | 75.43 (70.15-80.70) | .19 |
| Nonwhite | 73.87 (67.61-80.12) | 75.3 (69.61-80.98) | 66.84 (59.52-74.15) | 69.64 (65.36-73.91) | .69 |
| Sex | |||||
| Men | 74.74 (67.72-81.75) | 77.55 (71.59-83.50) | 72.49 (64.59-80.38) | 71.67 (66.22-77.11) | .89 |
| Women | 79.57 (75.78-83.35) | 84.74 (80.01-89.46) | 69.79 (65.47-74.10) | 74.91 (69.77-80.04) | .08 |
| With HbA1c <7% (good glycemic control) | |||||
| Overall | 55.24 (49.24-61.23) | 57.21 (50.89-63.52) | 54.67 (49.59-59.74) | 54.42 (49.87-58.96) | .99 |
| Age range, y | |||||
| 20-44 | 51.91 (35.05-68.76) | 44.38 (26.25-62.50) | 43.58 (24.54-62.61) | 52.12 (40.81-63.42) | .39 |
| 45-65 | 53.03 (45.58-60.47) | 55.27 (45.99-64.54) | 49.88 (43.94-55.81) | 50.5 (44.20-56.79) | .95 |
| >65 | 59.07 (49.62-68.51) | 63.09 (57.62-68.55) | 64.23 (56.76-71.69) | 60.23 (52.05-68.40) | .81 |
| Raceb | |||||
| White | 55.83 (48.57-63.08) | 59.6 (51.97-67.22) | 59.69 (52.71-66.66) | 55.86 (49.60-62.11) | .90 |
| Nonwhite | 54.15 (47.32-60.97) | 53.61 (43.77-63.44) | 47.38 (41.75-53.00) | 51.91 (47.53-56.28) | .86 |
| Sex | |||||
| Men | 55.21 (47.27-63.14) | 55.84 (46.00-65.67) | 53.47 (46.41-60.52) | 51.04 (45.49-56.58) | .29 |
| Women | 55.27 (47.56-62.97) | 58.65 (52.12-65.17) | 55.86 (49.58-62.13) | 57.67 (52.14-63.19) | .27 |
Abbreviations: IQR, interquartile range; NHANES, National Health and Nutrition Examination Survey.
Number of participants is unweighted. Survey weights for each period were used to calculate the proportions. We used weights specific to laboratory tests to calculate the values.
Race was examined as a subgroup for analysis assuming an association between HbA1c test or target awareness and race. Participants self-reported race and ethnicity by categories defined in NHANES; for this study, race was classified as nonwhite (Mexican American, other Hispanic, non-Hispanic black, other race, including multiracial in the original questionnaire) and white (non-Hispanic white in the original questionnaire).
Table 2. Hemoglobin A1c (HbA1c) Testing and Awareness of Test Results and Targets Among Participants Reporting Diabetesa.
| Participants, Weighted % (95% CI) by NHANES Period | |||
|---|---|---|---|
| 2007-2008 (n = 777) |
2011-2012 (n = 708) |
2013-2014 (n = 737) |
|
| With ≥1 HbA1c Test in the Past Yearb | |||
| Overall | 55.10 (49.69-60.50) | 69.56 (64.91-74.20) | 77.78 (75.07-80.48) |
| Age range, y | |||
| 20-44 | 63.68 (53.40-73.95) | 64.64 (55.31-73.96) | 75.17 (56.07-94.26) |
| 45-65 | 53.85 (46.42-61.27) | 73.17 (67.30-79.03) | 79.07 (75.79-82.34) |
| >65 | 53.82 (46.43-61.20) | 66.92 (59.23-74.60) | 77.1 (72.86-81.33) |
| Racec | |||
| White | 62.22 (55.14-69.29) | 75.45 (69.43-81.46) | 83.56 (78.13-88.98) |
| Nonwhite | 42.43 (36.19-48.66) | 61.25 (54.35-68.14) | 68.11 (63.50-72.71) |
| Sex | |||
| Male | 57.89 (51.75-64.02) | 70.69 (64.71-76.66) | 78.1 (74.19-82.00) |
| Female | 52.61 (45.33-59.88) | 68.46 (60.40-76.51) | 77.48 (73.05-81.90) |
| Aware of Past-Year HbA1c Result | |||
| Overall | 52.32 (47.63-57.00) | 64.71 (60.02-69.39) | 74.31 (69.63-78.99) |
| Age range, y | |||
| 20-44 | 64.88 (51.09-78.67) | 73.30 (59.50-87.09) | 72.44 (58.64-86.23) |
| 45-65 | 54.05 (44.73-63.37) | 67.22 (57.90-76.54) | 77.72 (68.40-87.04) |
| >65 | 46.14 (34.73-57.54) | 58.58 (47.17-69.98) | 70.60 (59.19-82.00) |
| Racec | |||
| White | 58.87 (52.26-65.47) | 72.36 (65.75-78.96) | 80.84 (74.24-87.45) |
| Nonwhite | 37.16 (29.25-45.07) | 51.40 (43.49-59.31) | 60.89 (52.98-68.80) |
| Sex | |||
| Male | 59.49 (52.11-66.86) | 66.71 (59.33-74.08) | 74.39 (67.01-81.76) |
| Female | 46.40 (41.03-51.76) | 62.70 (57.34-68.07) | 74.23 (68.87-79.60) |
| Aware of Target HbA1c Level Told by a Physician | |||
| Overall | 74.07 (70.48-77.66) | 83.95 (80.37-87.54) | 89.70 (86.11-93.29) |
| Age range, y | |||
| 20-44 | 86.22 (76.28-96.15) | 86.14 (76.20-96.08) | 86.83 (76.89-96.77) |
| 45-65 | 73.80 (66.97-80.64) | 85.30 (78.46-92.13) | 89.76 (82.92-96.60) |
| >65 | 70.29 (61.94-78.63) | 81.47 (73.12-89.81) | 90.63 (82.28-98.97) |
| Racec | |||
| White | 76.84 (72.16-81.52) | 89.94 (85.26-94.62) | 94.13 (89.45-98.81) |
| Nonwhite | 67.66 (61.04-74.28) | 73.53 (66.91-80.15) | 80.60 (73.98-87.21) |
| Sex | |||
| Male | 74.54 (67.93-81.16) | 89.44 (82.82-96.05) | 87.96 (81.35-94.57) |
| Female | 73.68 (69.39-77.97) | 78.45 (74.16-82.75) | 91.37 (87.07-95.66) |
Abbreviation: NHANES, National Health and Nutrition Examination Survey.
Data were not available in the 2009-2010 NHANES survey. Number of participants is unweighted. P value for the trend analysis was less than .001 for all rows except for patients aged 20 to 44 years. For this subgroup the P values were .02 for HbA1c testing, .16 for awareness of HbA1c result, and .81 for awareness of the target HbA1c level. Survey weights for each period were used to calculate the proportions. We used sample interview weights for the analysis related to the values.
Self-reported.
For the classification of race, see the footnotes in Table 1.
Discussion
The improvement in glycemic control between 1998 and 2010 among patients with diabetes appears to have plateaued during 2007-2014. Approximately 1 in 7 patients with diabetes had poor glycemic control (ie, HbA1c level >9%) throughout the study period despite an increase in the frequency of self-reported HbA1c testing and patient awareness of HbA1c result and patient-specific targets. One potential explanation is that in 2012 the American Diabetes Association set a higher target HbA1c level (8%) for people who are older, frail, and have many comorbidities or diabetes complications; however, no change in glycemic control was found in the elderly subgroup in this study. Individualization of the target HbA1c level may explain the improvement in HbA1c testing and awareness of HbA1c targets over time in all subgroups except for patients younger than 45 years. Therefore, focusing attention on this subgroup may be important especially because they would benefit most from treatment. Limitations of this study included the cross-sectional study design; therefore, inferences should be made cautiously.
Section Editor: Jody W. Zylke, MD, Deputy Editor.
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