Table 2.
Performance of Cystatin C and Creatinine-Based Estimating Equations Developed in 3134 People with CKD
| Model | Difference
|
Percent Difference
|
P30 (95% CI) | RMSE (95% CI) | ||
|---|---|---|---|---|---|---|
| Median (95% CI) | IQR (95% CI) | Median (95% CI) | IQR (95% CI) | |||
| External Validation (n=438) | ||||||
|
| ||||||
| 1. Cystatin C | −3 (−3, −2) | 8 (7, 9) | −10 (−13, −7) | 31 (28, 36) | 73 (72,74) | 0.264 (0.239, 0.289) |
| 2. Cystatin C, age, sex, and race | −2 (−2, −1) | 8 (7, 9) | −6 (−8, −4) | 30 (26, 32) | 79 (78,80) | 0.248 (0.223, 0.271) |
| 3. Creatinine, age, sex, and race | 2 (1,3) | 8 (7, 9) | 7 (4,9) | 25 (22, 29) | 84 (83,85) | 0.229 (0.210, 0.247) |
| 4. Cysatin C and creatinine, age, sex, and race | 0 (0,1) | 7 (6, 8) | 1 (−1,3) | 22 (20, 25) | 90 (89,91) | 0.193 (0.174, 0.211) |
Note: The difference is calculated as measured GFR - estimated GFR. Units are in mL/min/1.73 m2. Percent difference calculated as (measured GFR - estimated GFR)/measured GFR, and units are in percent. Median values measure bias and IQRs measure precision. To convert GFR from mL/min/1.73 m2 to mL/s/1.73 m2, multiply by 0.01666. Used with permission [36].
Abbreviations: P30, percentage of estimated GFR within 30% of mGFR; IQR, interquartile range; RMSE, root mean square error; CI, confidence interval; MDRD, Modification of Diet in Renal Disease; eGFR, estimated glomerular filtration; mGFR, measured glomerular filtration rate.
The 95% CI around the estimates of bias, IQR, P30, and RMSE provides the range of values likely to include parameter in 95% of circumstances. Comparison of CIs around any metric for 2 equations provides information about difference between them. If the 2 metrics were the same, the chance that the upper and lower bounds of the CIs would overlap is less than 5%; therefore, it can be concluded that they are statistically significantly different.