In SMART and MESA, for consenting participants, specimens stored at baseline were used to measure the biomarkers. In CARDIA, samples obtained during follow-up were used. EDTA plasma specimens were collected and were shipped frozen to a central repository where they were stored at −70° Centigrade.
The biomarkers for SMART, MESA and CARDIA were measured by the Laboratory for Clinical Biochemistry Research at the University of Vermont. hsCRP was measured using the BNII nephelometer (N High Sensitivity CRP; Siemens Healthcare Diagnostics, Deerfield, IL). The lower limit of detection was 0.16 μg/mL. IL-6 was measured by ultra-sensitive ELISA (Quantikine HS Human IL-6 Immunoassay; R&D Systems, Minneapolis, MN). The lower limit of detection was 0.16 pg/mL. For D-dimer, an immuno-turbidimetric assay (Liatest D-DI; Diagnostica Stago, Parsippany, NJ) was used on a Sta-R analyzer (Diagnostica Stago, Parsippany, NJ). The lower limit of detection of the assay was 0.01 μg/mL. A BNII nephelometer (Siemens Healthcare Diagnostics, Deerfield, IL) that utilized a particle-enhanced immunonephelometric assay (N Latex Cystatin-C) was used to assay cystatin C. The assay range is 0.195 to 7.330 mg/dl. The biological and laboratory variability of these assays has been described. Intra-assay coefficients of variation (CV) for IL-6, hsCRP, D-dimer are 6.3%, 8.9%, and 12.2%. For cystatin-C, the CV ranges from 2.0–2.8%.9 (link),10 (link),11 (link),12 (link),13 (link) Based on 3 to 4 controls per assay, inter-assay CVs range from 7–15% for IL-6, 3–6% for hsCRP, 5–14% for D-dimer and 2–6% for cystatin C (personal communication, Elaine Cornell).
The biomarkers for SMART, MESA and CARDIA were measured by the Laboratory for Clinical Biochemistry Research at the University of Vermont. hsCRP was measured using the BNII nephelometer (N High Sensitivity CRP; Siemens Healthcare Diagnostics, Deerfield, IL). The lower limit of detection was 0.16 μg/mL. IL-6 was measured by ultra-sensitive ELISA (Quantikine HS Human IL-6 Immunoassay; R&D Systems, Minneapolis, MN). The lower limit of detection was 0.16 pg/mL. For D-dimer, an immuno-turbidimetric assay (Liatest D-DI; Diagnostica Stago, Parsippany, NJ) was used on a Sta-R analyzer (Diagnostica Stago, Parsippany, NJ). The lower limit of detection of the assay was 0.01 μg/mL. A BNII nephelometer (Siemens Healthcare Diagnostics, Deerfield, IL) that utilized a particle-enhanced immunonephelometric assay (N Latex Cystatin-C) was used to assay cystatin C. The assay range is 0.195 to 7.330 mg/dl. The biological and laboratory variability of these assays has been described. Intra-assay coefficients of variation (CV) for IL-6, hsCRP, D-dimer are 6.3%, 8.9%, and 12.2%. For cystatin-C, the CV ranges from 2.0–2.8%.9 (link),10 (link),11 (link),12 (link),13 (link) Based on 3 to 4 controls per assay, inter-assay CVs range from 7–15% for IL-6, 3–6% for hsCRP, 5–14% for D-dimer and 2–6% for cystatin C (personal communication, Elaine Cornell).
