Table 4. Quality Results during the EDIC Study (1994–2014).
| BIOCHEMICAL SAMPLES | Variability (Coefficient of Variation) | Reliability (Coefficient of Reliability) | |||
| Serum | |||||
| Glycosylated hemoglobin | 0.48 | 0.998 | |||
| Creatinine | 2.14 / 1.28 | 0.982 / 0.998 | |||
| Cholesterol | 1.3 | 0.998 | |||
| Triglycerides | 2.3 | 0.981 | |||
| HDL-Cholesterol | 1.8 | 0.998 | |||
| LDL-Cholesterol | 2.1 | 0.989 | |||
| Urine | |||||
| Creatinine a , b | 3.0 / 2.69 | 0.969 / 0.99 | |||
| Albumin a , b | 10.2 / 5.18 | 0.972 / 0.999 | |||
| Albumin Excretion Rate a | 13.5 | 0.963 | |||
| Albumin-Creatinine Ratio b , c | 8.91 / 6.24 | 0.997 / 1.000 | |||
| Creatinine Clearance a | 4.3 | 0.937 | |||
| FUNDUS PHOTOGRAPHY | |||||
| Image Quality (%) | Excellent | Fair | Borderline | Unreadable | |
| April 1994–August 2008 d | (n = 12,724) | 58 | 34 | 8 | 1 |
| High | Adequate | Inadequate | |||
| September 2008–December 2014 e | (n = 3,016) | 82 | 16 | 2 | |
| Diabetic Retinopathy Severity Reproducibility f (%) | Weighted kappa (95% CI) | Exact agreement | Agreement within 1 level | Agreement within 2 levels | |
| Temporal Drift 2013 | (n = 156) | 0.8 (0.74, 0.86) | 66 | 91.7 | 94.9 |
| ELECTROCARDIOGRAM (%) | No quality issues | Minor technical, readable | Unreadable | ||
| January 1994–December 2014 | (n = 25,761) | 93 | 6 | 1 | |
a 4-hour timed urine collections (April 1994 –August 2012)
b Single random urine collections (August 2012 –December 2014)
c Single random urine collections (August 2004 –April 2013)
d During the DCCT through 2008 in EDIC, fundus photo quality was assessed using a 4-tier grading system.
e In 2008, the photo image quality control program expanded to include confidence scoring that allowed the graders to indicate their confidence in the grading of ocular disease as impacted by the quality of the photo set. High—no significant quality issue; Adequate—suboptimal quality interferes with grading; Inadequate—quality that prevents determination of major disease parameters. (CORU internal white paper: Image Confidence Scores, effective 04 Feb 2008).
f Annual re-read of 100 photo pairs across the spectrum of retinopathy severity performed by the CORU to evaluate reproducibility of scoring over time. 2013 Kappa scores consistent with previous photo re-reads.