Screening yield in DPP
summarizes the actual flow of participants through the screening process. shows the yield of the OGTT with regard to IGT-EFG and other states of abnormal glucose tolerance using the first OGTT performed for each participant. Of the 30,383 completed oral glucose tolerance tests, 12,490 (41.1%) produced local results that did not meet criteria for shipping to the CBL. Regression analyses described in the research design and methods section were used to convert local results into CBL-equivalent results. The other 17,893 (58.9%) produced local results that met shipping criteria, allowing CBL results to be used for classification.
Glucose tolerance status in 30,383 people screened by the DPP who underwent OGTT by source of data
As planned, the majority of OGTTs with local results only were classified as low risk (82.8%) or diabetic (9.5%). However, an estimated 7.7% of tests with local results only would have met DPP glucose eligibility criteria if they had been sent to the CBL. Although imperfect, these rules produced an enriched sample for shipment to the CBL, because 40.8% met glucose eligibility criteria for DPP and 15.4% had newly discovered diabetes (, column 3). We then pooled glucose tolerance data from these two groups to determine overall OGTT yields. After pooling, 27.2% had IGT-EFG and 13.0% had newly discovered diabetes.
The relation of screening yield to baseline characteristics
summarizes the relationships of selected baseline characteristics to screening yields. There was no sex difference in the overall yield of IGT-EFG or newly discovered diabetes. Both age and BMI were strongly and positively associated with the yield of IGT-EFG and with yield of IGT-EFG or newly discovered diabetes. Family history of diabetes was not associated with higher yields; in fact, the yield of IGT-EFG or of the combination of IGT-EFG or newly discovered diabetes was slightly lower in those who reported a family history than in those who reported no such history. Screening yields were similar in whites, African Americans, and Hispanics but were significantly higher in Asian/Pacific Islanders and lower in American Indians. Similar patterns were observed when risk factors were stratified by ethnic group (data not shown). In whites, African Americans, and Hispanics, age and BMI showed strong positive associations. In Asian/Pacific Islanders, age also showed a strong association with yield, but the relationship with BMI was markedly attenuated. In American Indians, there was virtually no association of age or BMI with screening yield, but these analyses were limited by smaller numbers.
Figure 2 Yield of abnormal glucose tolerance in 30,383 people screened by the DPP who underwent OGTT by sex, age, BMI, family history of diabetes, and ethnicity. Black bars indicate IGT-EFG (fasting glucose 95–125 mg/dl and 2-h glucose 140–199 (more ...)
Step 1 glucose as a predictor of yield
shows yield of IGT-EFG alone and IGT-EFG or newly discovered diabetes by step 1 glucose after stratification for method and timing of the measurement. Fasting venous glucose as measured by glucose analyzer was strongly associated with the yield of IGT-EFG (rising linearly from 12% to a maximum of 54% as step 1 glucose varied from 80 mg/dl to 129 mg/dl) and with the yield of IGT-EFG or newly discovered diabetes (rising almost linearly from 12 to 100% (). Fasting capillary glucose performed nearly as well. For fasting capillary glucose measured on the same day as the OGTT, the yield of IGT-EFG reached a maximum of 42% at a step 1 glucose of 105–109 mg/dl, and yield of IGT-EFG or newly discovered diabetes rose linearly from 14 to 96% as step 1 glucose varied from 80 to 124 mg/dl (). Nearly identical yields were observed for fasting capillary glucose measured 1–90 days before the OGTT (). There were insufficient nonfasting capillary glucose data for analysis.
Figure 3 Yield of abnormal glucose tolerance by fasting step 1 glucose. □ , IGT-EFG (see legend for definition). ♦, IGT-EFG plus newly diagnosed diabetes. A: Fasting venous glucose (analyzer) on the same day as the OGTT. B: Fasting capillary (more ...)
The three strongest correlates of yield were age, BMI, and step 1 glucose. We explored screening yield stratified by age or BMI using fasting capillary glucose measured 1–90 days before the OGTT, because this approach might be the most attractive for prescreening in populations. At levels of step 1 glucose below 100–105 mg/dl, both older age and higher BMIs were associated with an approximate doubling of yield of IGT-EFG and IGT-EFG or newly diagnosed diabetes. However, at levels exceeding 105 mg/dl, neither age nor BMI added predictive value beyond step 1 glucose (data not shown).
Multivariate analyses of yield
Finally, we determined the independent associations of the full range of step 1 variables with screening yield among the 5,276 participants who had a fasting capillary glucose measured 1–90 days before the OGTT, using multiple logistic regression (). In models without capillary glucose, age was strongly related to IGT-EFG. Compared with individuals aged < 40 years, those aged 60 and older were about twice as likely to have IGT-EFG. The relationship of age with IGT-EFG or diabetes was even stronger: compared with individuals aged < 40 years, those aged 60 and older were over four times more likely to have either condition. These associations were independent of sex, ethnicity, BMI, and family history and were only slightly attenuated by additional adjustment for step 1 capillary glucose measured 1–90 days before the OGTT. BMI showed a similarly strong, graded, independent association with both outcomes.
Adjusted relative odds (95% CI) of IGT-EFG and IGT-EFG or diabetes in 5,276 people screened by the DPP by selected characteristics, with and without fasting capillary glucose obtained 1–90 days prior to OGTT as an independent variable
Only Asian/Pacific Islanders had a significantly different pattern of screening yields, with a 70–80% greater odds of IGT-EFG, but over fourfold greater odds of IGT-EFG or diabetes, adjusted for other risk factors. Yields in African Americans, Hispanics, American Indians, and individuals of other ethnic groups were otherwise similar to yields in whites.
Family history of diabetes was weakly associated with both outcomes adjusted for other risk factors. Sex was not a consistent predictive factor.
Step 1 capillary glucose measured 1–90 days before the OGTT showed a powerful association with IGT-EFG or newly discovered diabetes. Compared with participants with step 1 glucose of 80–89 mg/dl, those with step 1 glucose of 120–129 mg/dl were 50 times as likely to have either IGT-EFG or diabetes. Despite the strength of this association, introduction of step 1 glucose into the combined outcome model produced little or no attenuation of the predictive value of other readily assessed characteristics.
The relationship of step 1 capillary glucose with IGT-EFG was more complex. Compared with participants with step 1 glucose of 80–89 mg/dl, those in the 100- to 109-mg/dl range were about twice as likely to have IGT-EFG, but those ≥ 130 mg/dl were only one-fifth as likely to have IGT-EFG, because a much higher proportion of these participants met criteria for diabetes. Again, introduction of step 1 glucose into the IGT-EFG models produced little or no attenuation of the predictive value of other characteristics.