Table 5.
Performance by subgroups defined by age, sex, race and eGFR in the entire dataset
| Group | N | Difference | Percent Difference | P30 | RMSE | |||
|---|---|---|---|---|---|---|---|---|
| Median (95% CI)* | IQR | Median | IQR | |||||
| Cystatin alone | ||||||||
| Overall | 3418 | 0.2 (−0.1, 0.6) | 11.7 | 0.7(−0.2,1.4) | 29.8 | 81 | 0.246 | |
| <40 | 666 | 0.9 (0.2, 1.9) | 13.9 | 2.7 (0.8,4.3) | 29.6 | 80 | 0.266 | |
| 40–65 | 2152 | 0.5 (0.1, 1.0) | 11.5 | 1.3(0.3,2.5) | 28.8 | 82 | 0.238 | |
| Age | >65 | 600 | −1.4 (−1.9, −0.6) | 11.0 | −3.7(−6.5,−1.8) | 32.7 | 79 | 0.252 |
| Y | 1261 | −2.1 (−2.9, −1.6) | 11.6 | −5.8(−7.1,−4.0) | 33.2 | 76 | 0.263 | |
| Female | N | 2157 | 1.5 (1.0, 1.9) | 11.2 | 3.5(2.7, 4.5) | 26.2 | 84 | 0.236 |
| White and other | 1610 | −0.8 (−1.2, −0.4) | 9.7 | −2.5(−3.7,−1.3) | 31.2 | 79 | 0.251 | |
| Race | African American | 1808 | 1.5 (1.0, 2.0) | 13.7 | 3.3(2.0,4.4) | 27.2 | 83 | 0.242 |
| Cystatin +age +race +sex | ||||||||
| Overall | 3418 | 0 (−0.2, 0.4) | 11.2 | 0.1(−0.6,1.0) | 28.2 | 83 | 0.239 | |
| <40 | 666 | −0.7 (−1.7, 0.1) | 12.5 | −2(−4.1,0.2) | 30.3 | 80 | 0.263 | |
| 40–65 | 2152 | 0.5 (−0.1, 0.9) | 10.8 | 1(−0.2,2.2) | 27.0 | 84 | 0.229 | |
| Age | >65 | 600 | −0.1 (−0.5, 0.6) | 11.1 | −0.3(−1.9,1.7) | 30.4 | 82 | 0.245 |
| Y | 1261 | 0.0 (−0.6, 0.6) | 11.7 | −0.1(−1.5,1.3) | 31.3 | 81 | 0.253 | |
| Female | N | 2157 | 0.1 (−0.3, 0.5) | 10.9 | 0.3(−0.7,1.6) | 26.7 | 84 | 0.230 |
| White and other | 1610 | −0.2 (−0.6, 0.3) | 9.7 | −0.6(−1.7,0.9) | 30 | 83 | 0.243 | |
| Race | African American | 1808 | 0.3 (−0.2, 0.9) | 13.5 | 0.6(−0.4,2.0) | 27.1 | 83 | 0.235 |
| Cystatin +creatinine + age + sex+ race | ||||||||
| Overall | 3418 | 0.1 (−0.3, 0.3) | 9.2 | 0.1(−0.7,0.9) | 23 | 89 | 0.197 | |
| <40 | 666 | −0.9(−1.5, −0.3) | 9.3 | −2.2(−4.0,−0.7) | 23.1 | 88 | 0.207 | |
| 40–65 | 2152 | 0.4(0.1, 0.7) | 9.2 | 1.0(0.2,1.9) | 22.3 | 90 | 0.194 | |
| Age | >65 | 600 | −0.3(−0.6, 0.4) | 8.7 | −0.9(−2.2,1.5) | 22.9 | 89 | 0.197 |
| Y | 1261 | −0.2(−0.5, 0.2) | 9.5 | −0.6(−1.6,0.8) | 25 | 87 | 0.210 | |
| Female | N | 2157 | 0.2(−0.2, 0.5) | 8.9 | 0.6(−0.6,1.1) | 21.7 | 91 | 0.189 |
| White and other | 1610 | −0.1(−0.4, 0.2) | 7.4 | −0.6(−1.4,0.7) | 22.2 | 90 | 0.192 | |
| Race | African American | 1808 | 0.4(−0.3, 0.9) | 11.3 | 0.7(−0.6,1.9) | 23.3 | 89 | 0.202 |
| Creatinine +age +race +sex | ||||||||
| Overall | 3418 | 0.1(−0.1, 0.3) | 10.8 | 0.3(−0.5, 0.9) | 26.9 | 85 | 0.226 | |
| <40 | 666 | −0.3(−1.0, 0.3) | 11.3 | −0.8(−2.5, 0.7) | 27.1 | 83 | 0.235 | |
| 40–65 | 2152 | 0.2(−0.1, 0.5) | 10.9 | 0.6(−0.3, 1.4) | 26.4 | 85 | 0.226 | |
| Age | >65 | 600 | 0(−0.6, 0.6) | 10.1 | 0.1(−2.2, 1.5) | 28.2 | 87 | 0.217 |
| Y | 1261 | −0.1(−0.5, 0.2) | 10.3 | −0.4(−1.7, 0.7) | 28.3 | 83 | 0.239 | |
| Female | N | 2157 | 0.2(−0.1, 0.5) | 11.1 | 0.7(−0.3, 1.3) | 26 | 86 | 0.219 |
| White and other | 1610 | 0(−0.3, 0.3) | 8.2 | 0.1(−0.9, 1.0) | 26.1 | 85 | 0.220 | |
| Race | African American | 1808 | 0.1(−0.3, 0.7) | 13.7 | 0.4(−0.8, 1.3) | 27.6 | 84 | 0.232 |
Difference is calculated as measured GFR-estimated GFR. Units are in mL/min per 1.73 m2. To convert GFR from mL/min/1.73 m2 to mL/sec per 1.73 m2, multiply by 0.01666. Percent difference is calculated as (measured GFR-estimated GFR)/measured GFR, and units are in percent. Median values measure bias and the inter-quartile ranges (IQR) measure precision. P30 is calculated as the percentage of estimated GFR within 30% of measured GFR. GFR, glomerular filtration rate; RMSE, root mean square error; CI, confidence interval.
The 95% confidence interval around the estimates of bias, IQR, P30 and RMSE provides the range of values which is likely to include the parameter in 95% of circumstances. Comparison of confidence intervals around any metric for two equations provides information as to difference between them. If the two metrics were the same, the chance that the upper and lower bounds of the confidence intervals would not overlap is less than 5%. Therefore, it can be concluded that they are statistically significantly different.