Table 2.
Bias, P30, interquartile range and correct classification of different Chronic Kidney Disease Epidemiology Collaboration eGFR equations, overall and stratified by the magnitude and direction of the discordance between eGFRcr and eGFRcys
| Metrics | Total Population | eGFRcys<eGFRcra | eGFRcys≈eGFRcra | eGFRcys>eGFRcra |
|---|---|---|---|---|
| eGFRcys >20% Lower Than eGFRcr | eGFRcys Within 20% of eGFRcr | eGFRcys >20% Higher Than eGFRcr | ||
| eGFRcrb | ||||
| Bias, median difference (ml/min per 1.73 m2)c | 8.7 (8.4–9.0) | 15.0 (14.6–15.5) | 4.5 (4.1–4.8) | −4.5 (−5.3 to −3.8) |
| P30 (%)b | 68.8 (67.8–69.7) | 49.7 (48.3–51.2) | 86.0 (84.9–87.0) | 85.9 (83.2–88.3) |
| IQR, ml/min per 1.73 m2d | 18.6 (0.2–18.8) | 17.5 (7.0–24.5) | 15.1 (−2.0 to 13.1) | 12.3 (−13.0 to −0.7) |
| Correct classification (%)e | 52.6 (51.6–53.6) | 38.1 (36.7–39.5) | 66.5 (65.1–67.9) | 61.9 (58.3–65.4) |
| eGFRcysb | ||||
| Bias, median difference (ml/min per 1.73 m2)c | −2.3 (−2.6 to −2.0) | −8.6 (−9.0 to −8.3) | 2.1 (1.7–2.4) | 8.4 (7.3–10.0) |
| P30f | 80.7 (79.9–81.5) | 72.9 (71.6–74.2) | 90.4 (89.5–91.3) | 71.8 (68.4–75.1) |
| IQR, ml/min per 1.73 m2d | 15.6 (−10.5 to 5.1) | 14.2 (−16.5 to −2.3) | 13.8 (−4.0 to 9.9) | 16.5 (2.5–19.0) |
| Correct classificatione | 57.4 (56.4–58.4) | 45.4 (43.9–46.8) | 69.2 (67.8–70.5) | 62.9 (59.4–66.6) |
| eGFRcr-cysb | ||||
| Bias, median difference (ml/min per 1.73 m2)c | 2.5 (2.2–2.7) | 0.7 (0.4–1.0) | 5.0 (4.6–5.4) | 1.8 (1.2–2.5) |
| P30b | 86.4 (85.7–87.1) | 84.3 (83.2–85.4) | 88.3 (87.3–89.3) | 87.8 (85.4–90.2) |
| IQR, ml/min per 1.73 m2d | 13.6 (−3.5–10.0) | 12.6 (−5.5–7.1) | 14.5 (−1.4–13.2) | 12.3 (−2.6–9.6) |
| Correct classificatione | 65.4 (64.5–66.4) | 61.6 (60.2–63) | 68.4 (67–69.7) | 71.9 (68.6–75.2) |
Cr, creatinine; cys, cystatin C; IQR, interquartile range; mGFR, measured GFR.
A measurement fell within eGFRcys<eGFRcr when eGFRcys was more than 20% lower than eGFRcr; eGFRcys≈eGFRcr if the difference between eGFR values was within 20% of eGFRcr; and within eGFRcys>eGFRcr when eGFRcys was more than 20% higher than eGFRcr.
eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration 2012 and 2021 equations.
Bias was expressed as the median difference in eGFR minus measured GFR (95% confidence interval). A negative bias indicates underestimation of the measured GFR, and a positive bias indicates overestimation of the measured GFR.
Interquartile range is defined as the interquartile range and a measure of precision (the dispersion of individual errors around the median bias).
Correct classification of GFR categories was defined as agreement of eGFR and measured GFR categories using the Kidney Disease Improving Global Outcomes GFR categories (<15, 15–29, 30–44, 45–59, 60–89 and ≥90 ml/min per 1.73 m2).
P30 was defined as the percentage of individuals with eGFRs within 30% of measured GFR (95% confidence interval).