Glomerular Filtration Rate Estimation
Glomerular Filtration Rate Estimation
Table 1 shows the demographic and clinical characteristics of the participants overall and stratified by level of eGFRcr. The mean (SD) measured GFR was 69.8 (41.0) mL/min/1.73 m; 20.7% were >65 years, 40.8% were women, 53.1% had diabetes and 7.2% had BMI <20 kg/m. Participants with higher levels of eGFRcr were younger, and had a higher proportion with diabetes.
Table 2 compares the bias and absolute difference of eGFRcr, eGFRcys and eGFRcr-cys overall and stratified by the level of eGFRcr. Overall, bias was similar for the three equations. For all the three equations, bias was higher at higher levels of eGFRcr, and differences among subgroups appeared to be greater at higher eGFRcr. eGFRcr underestimated mGFR more for younger versus older people and in people with versus without diabetes (Figure 1). eGFRcr underestimated mGFR more for people with higher BMI and overestimated mGFR for people with BMI <20 kg/m. In contrast, eGFRcys underestimated mGFR more for older versus younger people and in people with higher BMI (Figure 2). For eGFRcr-cys, differences among subgroups in bias were intermediate between those observed for eGFRcr and eGFRcys (Figure 3).
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Figure 1.
Bias of eGFRcr by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcr). eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
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Figure 2.
Bias of eGFRcys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcys). eGFRcys, estimated glomerular filtration rate based on serum cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
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Figure 3.
Bias of eGFRcr-cys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcr-cys). eGFRcr-cys, estimated glomerular filtration rate based on serum creatinine and cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
Bias of eGFRcys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcys). eGFRcys, estimated glomerular filtration rate based on serum cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
The mean absolute difference was smaller for eGFRcr-cys than for eGFRcr and eGFRcys at all levels of eGFRcr ( Table 2 ). Table 3 (Column 1) compares the difference in absolute difference of eGFRcys with eGFRcr in the overall dataset and in subgroups; comparisons between subgroups stratified by eGFRcr are shown in Supplementary Table S1 and Figure S1. Overall, eGFRcr and eGFRcys had a similar absolute difference [difference of 0.2 (−0.4, 0.8) mL/min/1.73 m]; however, there were differences among some subgroups. eGFRcys had a smaller absolute difference than eGFRcr in people with diabetes [difference of 1.7 (0.9, 2.5)] and a larger absolute difference than eGFRcr in people without diabetes [difference of −1.4 (−2.3, −0.5) mL/min/1.73 m] (P < 0.001). Across BMI groups, there was a non-significant trend (P = 0.08) toward a smaller absolute difference for eGFRcys than eGFRcr at lower BMI and a larger absolute difference for eGFRcys than eGFRcr at higher BMI. The interaction of BMI with eGFRcr was significant (P = 0.03), so that among people with eGFRcr >90 mL/min/1.73 m, eGFRcys had a smaller absolute difference than eGFRcr for the subgroup with BMI <20 kg/m [n = 14, difference of 11.1 (0.4, 21.8) mL/min/1.73 m] but larger absolute difference than eGFRcr for the subgroup with BMI >30 kg/m [n = 34, difference of −4.9 (−9.8, −0.1) mL/min/1.73 m] (Supplementary Table S1).
Table 3 (Column 2), Supplementary Table S2 and Figure S2 compare the difference in absolute difference of eGFRcr-cys with eGFRcr. eGFRcr-cys had smaller absolute difference than eGFRcr overall [difference of 1.6 (1.3, 2.0) mL/min/1.73 m], and in all subgroups defined by eGFRcr, age, sex, diabetes status or BMI (except >30 kg/m). By comparing the difference in absolute difference between eGFRcr minus eGFRcr-cys (column 2) versus eGFRcr minus eGFRcys (Column 1), as well as in Supplementary Tables S2 versus S1, we found that eGFRcr-cys had smaller absolute difference than eGFRcr in the subgroups in which eGFRcys had smaller absolute difference than eGFRcr (people with diabetes and people with eGFRcr > 90 mL/min/1.73 m and BMI < 20 kg/m)
Table 3 (Column 3), Supplementary Table S3 and Figure S3 show that eGFRcr-cys had a smaller absolute difference than eGFRcys in the overall dataset [difference of 1.4 (1.1, 1.8) mL/min/1.73 m], and in all subgroups defined by eGFRcr categories, age, sex or BMI and in people without diabetes. eGFRcr-cys and eGFRcys were similar in people with diabetes. By comparing the difference in absolute difference between eGFRcys minus eGFRcr-cys (column 3) versus eGFRcr minus eGFRcys (column 1) and Supplementary Tables S3 versus S1, we found that eGFRcr-cys had a smaller absolute difference than eGFRcys in the subgroups in which eGFRcys had a larger absolute difference than eGFRcr (people without diabetes and people with eGFR > 90 mL/min/1.73 m and BMI > 30 kg/m).
Analyses using P20 and P30 as measures of accuracy revealed similar results (Supplementary Tables S4 and S5). Sensitivity analyses using mGFR (Supplementary Tables S6–S9) and eGFRcys rather than eGFRcr to categorize eGFR did not reveal substantially different results.
Results
Table 1 shows the demographic and clinical characteristics of the participants overall and stratified by level of eGFRcr. The mean (SD) measured GFR was 69.8 (41.0) mL/min/1.73 m; 20.7% were >65 years, 40.8% were women, 53.1% had diabetes and 7.2% had BMI <20 kg/m. Participants with higher levels of eGFRcr were younger, and had a higher proportion with diabetes.
Table 2 compares the bias and absolute difference of eGFRcr, eGFRcys and eGFRcr-cys overall and stratified by the level of eGFRcr. Overall, bias was similar for the three equations. For all the three equations, bias was higher at higher levels of eGFRcr, and differences among subgroups appeared to be greater at higher eGFRcr. eGFRcr underestimated mGFR more for younger versus older people and in people with versus without diabetes (Figure 1). eGFRcr underestimated mGFR more for people with higher BMI and overestimated mGFR for people with BMI <20 kg/m. In contrast, eGFRcys underestimated mGFR more for older versus younger people and in people with higher BMI (Figure 2). For eGFRcr-cys, differences among subgroups in bias were intermediate between those observed for eGFRcr and eGFRcys (Figure 3).
(Enlarge Image)
Figure 1.
Bias of eGFRcr by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcr). eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
(Enlarge Image)
Figure 2.
Bias of eGFRcys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcys). eGFRcys, estimated glomerular filtration rate based on serum cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
(Enlarge Image)
Figure 3.
Bias of eGFRcr-cys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcr-cys). eGFRcr-cys, estimated glomerular filtration rate based on serum creatinine and cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
Bias of eGFRcys by demographic and clinical characteristics of subgroups. Bias is calculated as the mean value of (mGFR − eGFRcys). eGFRcys, estimated glomerular filtration rate based on serum cystatin C; eGFRcr, estimated glomerular filtration rate based on serum creatinine; mGFR, measured glomerular filtration rate.
The mean absolute difference was smaller for eGFRcr-cys than for eGFRcr and eGFRcys at all levels of eGFRcr ( Table 2 ). Table 3 (Column 1) compares the difference in absolute difference of eGFRcys with eGFRcr in the overall dataset and in subgroups; comparisons between subgroups stratified by eGFRcr are shown in Supplementary Table S1 and Figure S1. Overall, eGFRcr and eGFRcys had a similar absolute difference [difference of 0.2 (−0.4, 0.8) mL/min/1.73 m]; however, there were differences among some subgroups. eGFRcys had a smaller absolute difference than eGFRcr in people with diabetes [difference of 1.7 (0.9, 2.5)] and a larger absolute difference than eGFRcr in people without diabetes [difference of −1.4 (−2.3, −0.5) mL/min/1.73 m] (P < 0.001). Across BMI groups, there was a non-significant trend (P = 0.08) toward a smaller absolute difference for eGFRcys than eGFRcr at lower BMI and a larger absolute difference for eGFRcys than eGFRcr at higher BMI. The interaction of BMI with eGFRcr was significant (P = 0.03), so that among people with eGFRcr >90 mL/min/1.73 m, eGFRcys had a smaller absolute difference than eGFRcr for the subgroup with BMI <20 kg/m [n = 14, difference of 11.1 (0.4, 21.8) mL/min/1.73 m] but larger absolute difference than eGFRcr for the subgroup with BMI >30 kg/m [n = 34, difference of −4.9 (−9.8, −0.1) mL/min/1.73 m] (Supplementary Table S1).
Table 3 (Column 2), Supplementary Table S2 and Figure S2 compare the difference in absolute difference of eGFRcr-cys with eGFRcr. eGFRcr-cys had smaller absolute difference than eGFRcr overall [difference of 1.6 (1.3, 2.0) mL/min/1.73 m], and in all subgroups defined by eGFRcr, age, sex, diabetes status or BMI (except >30 kg/m). By comparing the difference in absolute difference between eGFRcr minus eGFRcr-cys (column 2) versus eGFRcr minus eGFRcys (Column 1), as well as in Supplementary Tables S2 versus S1, we found that eGFRcr-cys had smaller absolute difference than eGFRcr in the subgroups in which eGFRcys had smaller absolute difference than eGFRcr (people with diabetes and people with eGFRcr > 90 mL/min/1.73 m and BMI < 20 kg/m)
Table 3 (Column 3), Supplementary Table S3 and Figure S3 show that eGFRcr-cys had a smaller absolute difference than eGFRcys in the overall dataset [difference of 1.4 (1.1, 1.8) mL/min/1.73 m], and in all subgroups defined by eGFRcr categories, age, sex or BMI and in people without diabetes. eGFRcr-cys and eGFRcys were similar in people with diabetes. By comparing the difference in absolute difference between eGFRcys minus eGFRcr-cys (column 3) versus eGFRcr minus eGFRcys (column 1) and Supplementary Tables S3 versus S1, we found that eGFRcr-cys had a smaller absolute difference than eGFRcys in the subgroups in which eGFRcys had a larger absolute difference than eGFRcr (people without diabetes and people with eGFR > 90 mL/min/1.73 m and BMI > 30 kg/m).
Analyses using P20 and P30 as measures of accuracy revealed similar results (Supplementary Tables S4 and S5). Sensitivity analyses using mGFR (Supplementary Tables S6–S9) and eGFRcys rather than eGFRcr to categorize eGFR did not reveal substantially different results.
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