During Wave IV, Add Health collected biological specimens from a large, nationally representative sample of young adults. Given the size of the Wave IV sample, its geographic distribution, and in-home setting of the respondent interviews, biological specimen collection involved practical, relatively non-invasive, cost-efficient and innovative methods. These methods included collection of capillary whole blood via finger prick by trained and certified field interviewers, its in situ desiccation, then shipment, assay and archival of dried blood spots. The collection of capillary whole blood followed the collection of cardiovascular and anthropometric measures (Entzel et al., 2009) and saliva (in preparation). It preceded the collection of data on respondent use of prescription and select over-the-counter medications (Tabor et al., 2010). Further details on the design of Add Health Waves I-IV, are available elsewhere (Harris, 2011). Included in the Add Health Wave IV data are two measures of glucose homeostasis based on assay of the dried blood spots: • Glucose (mg/dl) and • Hemoglobin A1c (HbA1c, %). To facilitate analysis and interpretation of HbA1c, the restricted-use Add Health Wave IV data also include a trichotomous flag distinguishing the original (0) from two types (1,2) of inter-converted assay results (see Section 188.8.131.52): • Convert (0,1,2) Moreover, the restricted-use Add Health Wave IV data include six constructed measures: • Fasting duration (h) • Classification of fasting glucose (ADA, 2011) • Classification of non-fasting glucose (ADA, 2011) • Classification of HbA1c (ADA, 2011) • Anti-diabetic medication use • Joint classification of glucose, HbA1c, self-reported history of diabetes, and anti-diabetic medication use. This document summarizes the rationale, equipment, protocol, assay, internal quality control, data cleaning, external quality control, and classification procedures for each measure listed above. Documentation of other (metabolic; inflammatory; immune; genetic) measures based on assay of the dried blood spots and genotyping of DNA extracted from salivary buccal cells will be provided in separate reports.