Abstract P010: Dried Capillary Whole Blood Spot-Based Hemoglobin A
1c
, Fasting Glucose, and Diabetes Prevalence in a Nationally Representative Population of Young U.S. Adults: Add Health, Wave IV
Authors: Whitsel Eric A , Nguyen Quynh C , Suchindran Chirayath M , Tabor Joyce W , Cuthbertson Carmen C , Wener Mark H , Potter Alan J , Killeya-Jones Ley , Hussey Jon M , Halpern Carolyn T , Harris Kathleen M 
Published: July 2021

Little is known about the biomarker-based prevalence of diabetes among U.S. adults aged 24-32 years, an age group historically characterized by low cardiovascular disease risk. We addressed the paucity of information within this age group among 15,701 participants at Wave IV of the National Longitudinal Study of Adolescent Health (Add Health, 2008), a study including nationally representative oversamples of racial / ethnic groups underrepresented by the National Health and Nutrition Examination Survey (NHANES). Capillary whole blood was collected via finger prick onto Whatman 903® Protein Saver cards by trained and certified field interviewers, desiccated, then shipped to central laboratories for assay and archival. Sensitivity of the glucose assay was 22 mg/dl. Assayed values in the lowest half percentile of the distribution were re-assayed. Re-assayed and original values were averaged. The within- and between-assay coefficients of variation (CVs) were 4.4% and 4.8%. For HbA
1c
, the corresponding sensitivity, within- and between-assay CVs were 3%, 2.2%, and 2.4%. In paired serum and blood spots, glucose concentrations (mg/dl) were strongly associated (n = 83; Pearson r = 0.97). Associations were equally strong for HbA
1c
(%) in paired whole blood and blood spots (n = 80; Pearson r = 0.99). In a race/ethnicity- and sex-stratified random sample of 100 Add Health participants among whom capillary whole blood was collected twice, one to two weeks apart, reliability of random (fasting ≥ 8 hr or non-fasting) glucose and HbA
1c
was estimated as an intra-class correlation coefficient and 95% confidence interval, ICC (95% CI): 0.39 (0.21, 0.58) and 0.97 (0.96-0.98). Add Health participants were more likely than similarly aged NHANES (2007-2008) participants to be native-born, insured, college educated, and overweight or obese. After weighting for unequal sampling probabilities and clustering, mean (standard deviation) HbA
1c
and fasting glucose were higher in Add Health than NHANES: 5.6% (0.8%) and 107 (35) mg/dl vs. 5.2% (0.5%) and 97 (14) mg/dl. The weighted prevalence (95% CI) of HbA
1c
≥ 6.5% and fasting glucose ≥ 126 mg/dl also were higher in Add Health than NHANES: 3.6% (2.9-4.3) and 10.3% (8.7%-12.2%) vs. 1.7% (0.9%-3.2%) and 2.1% (0.8%-5.5%). Corresponding odds ratios (95% CIs) were: 2.1 (1.1-3.9) and 5.2 (2.1-13.3). Adjustment for sociodemographic, clinical and behavioral risk factors attenuated the associations: 1.5 (0.8-3.1) and 4.2 (1.7-10.4). However, the addition of self-reported history of diabetes and use of anti-diabetics had relatively little effect on them. Carefully standardized, in-home collection of whole blood spots can yield valid and reliable estimates of glucose and HbA
1c
. Their interpretation in context of the prevalent obesity and hypertension at Add Health Wave IV reinforces suggestions that young, U.S. adults face a historically high risk of cardiovascular disease.