Table 1 GFR estimating equations used in the study

1.

The Modification Diet in Renal Disease (MDRD) equation [14]: 175 × Scr^‒ 1.154 × age^‒ 0.203 × 0.742(if female) × 1.212(if black); where Scr is serum creatinine, mg/dl; age in years.

2.

The Chronic Kidney Disease Epidemiology creatinine (CKD-Epi_cr) equation [15]: 141 × min(Scr/κ, 1)^a × max(Scr/κ, 1)^‒ 1.209 × 0.993^age × 1.018(if female) × 1.159(if black); where Scr is serum creatinine, k is 0.7 for females and 0.9 for males, α is -0.329 for females and -0.411 for males, min is the minimum of Scr/ k or 1, and max is the maximum of Scr/k or 1.

3.

The Chronic Kidney Disease Epidemiology cystatin C (CKD-Epi_cys) equation [16]: 133 × min(Scys/0.8, 1)^‒ 0.499 × max(Scys/0.8, 1)^‒ 1.328 × 0.996^age(×0.932 if female); where Scys is serum cystatin C, min indicates the minimum of Scr/κ or 1, and max indicates the maximum of Scys/κ or 1.

4.

The Chronic Kidney Disease Epidemiology creatinine-cystatin C (CKD-Epi_cr-cys) equation [16]: 135 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^‒ 0.601 × min(Scys/0.8, 1)^‒ 0.375 × max(Scys/0.8, 1)^‒ 0.711 × 0.995^age(×0.969 if female)(×1.08 if black); where Scr is serum creatinine, Scys is serum cystatin C, κ is 0.7 for females and 0.9 for males, α is -0.248 for females and -0.207 for males, min indicates the minimum of Scr/κ or 1, and max indicates the maximum of Scr/κ or 1.

5.

The Berlin Initiative Study creatinine (BIS_cr) equation [9]: 3736 × creatinine^‒ 0.87 × age^‒ 0.95 × 0.82(if female).

6.

The Berlin Initiative Study creatinine-cystatin C (BIS_cr-cys) equation [9]: 767 × cystatin C^‒ 0.61 × creatinine^‒ 0.40 × age^‒ 0.57 × 0.87(if female).