In clinical practice, it is critical to assess kidney function in a precise and accurate manner. Measurement of the glomerular filtration rate (GFR) is considered the best method that reflects kidney function, both in health and in disease [
Cystatin C has been proposed as a new endogenous marker of GFR. This low molecular weight cysteine-protease inhibitor (13,300 Da) is produced at a constant rate by all the nucleated cells of the human body [
A developed creatinine-cystatin C (combined) CKD-EPI equation has been tested by some studies. In one cross-sectional work which included 1119 participants from 5 different studies, Inker et al. concluded that the combined creatinine-cystatin C CKD-EPI equation performed better than those based on either of these markers alone and may be useful as a confirmatory test for CKD [
In turn, CKD is an important and growing public health problem worldwide. It is estimated that approximately 500,000,000 people present some degree of kidney dysfunction [
We decided to include the combined creatinine-cystatin C-based CKD-EPI equation and proteinuria measurements in the 300 patients previously studied and correlated them in terms of GFR at the different CKD stages. Finally, we also evaluated whether any correlation difference was encountered between proteinuria with either creatinine- or cystatin C-based equations at the different stages of CKD.
Prospective, cross-sectional, observational study was undertaken between October 2009 and September 2010 and reassessed with respect to other GFR equations and included proteinuria as another variable. This reassessment was undertaken in March 2013 at the Hospital Británico de Buenos Aires, Argentina. Three hundred adult patients were included.
The study was approved by the Institutional Review Board (approval number 338). Cystatin C kits were donated by Gentian, Inc., Oslo, Norway. Local permissions by the Ministry of Health and ANMAT-INAME were obtained (form 788/0509, May 13, 2009).
Three hundred Caucasian adult outpatients between 18 and 80 years were included. Gender: males, 174 (58%); females, 126 (42%). Chronic kidney disease and its stages were defined according to K/DOQI guidelines [
The following studies were performed: fasting serum creatinine and cystatin C, 24-hour creatinine clearance, 24-hour proteinuria,
GFR was estimated by serum creatinine, 24-hour creatinine clearance, CKD-EPI creatinine [
Creatinine was determined by dry chemistry sarcosine oxidase method with traceable calibration to mass spectrometry isotopic dilution using Vitros 5.1 FS autoanalyzer (
Creatinine clearance: determined adjusted to age, weight, and height according to DuBois body surface area equation. The correct urine collection was tested by Walser equation. Twenty-four-hour urine creatinine clearance:
GFR = urinary creatinine (mg/dL) (Serum creatinine (mg (dL))) × daily urinary output (1440) × DuBois body surface area (1.73 m2). CKD EPI:
In males, if creatinine ≤ 0.9, GFR = 141 × (plasmatic creatinine (0.9))−0.411 × 0.993age. In males, if creatinine > 0.9, GFR = 141 × (plasmatic creatinine (0.9))−1.209 × 0.993age. In females, if creatinine ≤ 0.7, GFR = 144 × (plasmatic creatinine (0.7))−0.329 × 0.993age. In females, if creatinine > 0.7, GFR = 144 × (plasmatic creatinine (0.7))−1.209 × 0.993age.
DuBois equation for body surface area calculation: BSA = 0.007184 × (weight kg)0.425 × (height cm)0.725. Walser formula:
Males 28.2 − (0.172 × age). Females 21.9 − (0.115 × age).
Hoek: GFR = −4.32 + 80.35 × 1 (Cystatin C). CKD EPI:
Female or male ≤0.8 133 × (cystatin C/0.8)−0.499 × 0.996age [× 0.932 if female]. Female or male >0.8 133 × (cystatin C/0.8)−1.328 × 0.996age [× 0.932 if female]. Combined CKD EPI:
If creatinine ≤ 0.7 or cystatin C ≤ 0.8
130 × (creatinine/0.7) − 0.248 × (cystatin C/0.8) − 0.375 × 0.995age. If cystatin C > 0.8
130 × (creatinine/0.7) − 0.248 × (cystatin C/0.8) − 0.711 × 0.995age.
If creatinine > 0.7 or ≤0.8
130 × (creatinine/0.7) − 0.601 × (cystatin C/0.8) − 0.375 × 0.995age. If cystatin C > 0.8
130 × (creatinine/0.7) − 0.601 × (cystatin C/0.8) − 0.711 × 0.995age.
135 × (creatinine/0.9) − 0.207 × (cystatin C/0.8) − 0.375 × 0.995age. If cystatin C > 0.8
135 × (creatinine/0.9) − 0.207 × (cystatin C/0.8) − 0.711 × 0.995age.
If creatinine > 0.9 or ≤0.8
135 × (creatinine/0.9) − 0.601 × (cystatin C/0.8) − 0.375 × 0.995age. If cystatin C > 0.8
135 × (creatinine/0.9) − 0.601 × (cystatin C/0.8) − 0.711 × 0.995age.
Results are expressed as the mean ± 2 standard deviations. Intergroup comparisons were analyzed with chi-square (
Population analysis and GFR estimations estimated by other equations are depicted in Tables
General data of certain variables at different stages of CKD.
Confidence interval for the mean at 95% | ||||||
---|---|---|---|---|---|---|
Group | Media | Lower limit | Upper limit | Standard deviation | Interquartile amplitude | |
BMI | Control | 23.95 | 22.690 | 25.217 | 3.68 | 2.63 |
1 | 25.74 | 23.982 | 27.503 | 4.36 | 7.56 | |
2 | 25.95 | 24.764 | 27.133 | 4.26 | 5.47 | |
3 | 26.95 | 26.007 | 27.888 | 4.49 | 6.45 | |
4 | 29.29 | 27.170 | 31.418 | 6.37 | 6.51 | |
5 | 26.38 | 25.160 | 27.593 | 4.71 | 6.12 | |
|
||||||
AGE | Control | 48.63 | 44.25 | 53.006 | 12.74 | 16.00 |
1 | 42.89 | 37.48 | 48.294 | 13.39 | 17.00 | |
2 | 45.23 | 41.41 | 49.051 | 13.72 | 18.75 | |
3 | 54.44 | 51.28 | 57.610 | 15.12 | 24.00 | |
4 | 63.22 | 58.47 | 67.963 | 14.24 | 14.50 | |
5 | 61.33 | 56.90 | 65.771 | 17.18 | 16.75 | |
|
||||||
PROTEINURIA | Control | .049 | .012 | .087 | .11 | .00 |
1 | .37 | .135 | .598 | .57 | .41 | |
2 | .31 | .183 | .426 | .43 | .40 | |
3 | 1.39 | .708 | 2.075 | 3.26 | 1.14 | |
4 | 1.87 | .808 | 1.560 | .99 | .71 | |
5 | 2.48 | 1.516 | 3.440 | 3.724 | 2.83 | |
|
||||||
99mTc-DTPA | Control | 81.53 | 73.308 | 89.753 | 13.94 | 29.57 |
1 | 95.26 | 88.605 | 101.944 | 15.80 | 15.77 | |
2 | 70.05 | 66.903 | 73.194 | 11.30 | 14.33 | |
3 | 45.59 | 43.624 | 47.556 | 9.39 | 14.27 | |
4 | 22.60 | 20.653 | 24.547 | 5.75 | 6.91 | |
5 | 11.18 | 8.989 | 13.364 | 8.40 | 9.79 | |
|
||||||
Cystatin C | Control | .748 | .717 | .780 | .092 | .120 |
1 | .824 | .724 | .925 | .249 | .172 | |
2 | .935 | .846 | 1.024 | .320 | .364 | |
3 | 1.32 | 1.199 | 1.437 | .569 | .645 | |
4 | 1.98 | 1.532 | 2.035 | .755 | .850 | |
5 | 4.03 | 3.666 | 4.397 | 1.414 | 2.268 |
Abbreviations: CKD: chronic kidney disease; BMI: body mass index.
Most frequent causes of CKD.
CKD etiology |
Group | ||||||||
---|---|---|---|---|---|---|---|---|---|
0 | 1 | 2 | 3 | 4 | 5 | Total |
|
| |
Hypertension | 0 | 10 | 28 | 56 | 33 | 48 | 175 | 80.30 |
|
Diabetes | 0 | 5 | 5 | 12 | 14 | 17 | 53 | 26.77 |
|
Glomerulonephritis | 0 | 9 | 18 | 30 | 10 | 18 | 85 | 20.65 |
|
PKD | 0 | 2 | 3 | 11 | 2 | 9 | 27 | 8.54 |
|
Abbreviations: CKD: chronic kidney disease; PKD: polycystic kidney disease.
Glomerular filtration rate measured by all approaches globally and by stages of chronic kidney disease.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined CKD-EPI | Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.8113 | 1 | |||||||
|
0 | ||||||||
Creatinine clearance | |||||||||
rho | 0.7847 | −0.8158 | 1 | ||||||
|
0 | 0 | |||||||
Hoek | |||||||||
rho | 0.7975 | −0.8749 | 0.8208 | 1 | |||||
|
0 | 0 | 0 | ||||||
Creatinine |
|||||||||
rho | 0.8397 | −0.9541 | 0.8365 | 0.9021 | 1 | ||||
|
0 | 0 | 0 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.798 | −0.8566 | 0.8172 | 0.9851 | 0.9105 | 1 | |||
|
0 | 0 | 0 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.8311 | −0.9231 | 0.845 | 0.9673 | 0.9728 | 0.978 | 1 | ||
|
0 | 0 | 0 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.791 | 0.876 | −0.8182 | −0.9928 | −0.9011 | −0.9918 | −0.9707 | 1 | |
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.4845 | 0.5273 | −0.4928 | −0.5309 | −0.5086 | −0.5241 | −0.5291 | 0.5433 | 1 |
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Global assessment correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined |
Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.8113 | 1 | |||||||
|
0 | ||||||||
Creatinine clearance | |||||||||
rho | 0.7847 | −0.8158 | 1 | ||||||
|
0 | 0 | |||||||
Hoek | |||||||||
rho | 0.7975 | −0.8749 | 0.8208 | 1 | |||||
|
0 | 0 | 0 | ||||||
Creatinine |
|||||||||
rho | 0.8397 | −0.9541 | 0.8365 | 0.9021 | 1 | ||||
|
0 | 0 | 0 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.798 | −0.8566 | 0.8172 | 0.9851 | 0.9105 | 1 | |||
|
0 | 0 | 0 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.8311 | −0.9231 | 0.845 | 0.9673 | 0.9728 | 0.978 | 1 | ||
|
0 | 0 | 0 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.791 | 0.876 | −0.8182 | −0.9928 | −0.9011 | −0.9918 | −0.9707 | 1 | |
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.4845 | 0.5273 | −0.4928 | −0.5309 | −0.5086 | −0.5241 | −0.5291 | 0.5433 | 1 |
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
As to proteinuria, it displayed the highest significant correlations with serum cystatin C (
Relevant differences emerged when groups were analyzed separately (Tables
Control group correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine CKD-EPI | Cystatin C CKD-EPI | Combined CKD-EPI | Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.3813 | 1 | |||||||
|
0.0238 | ||||||||
Creatinine clearance | |||||||||
rho | 0.4145 | −0.4519 | 1 | ||||||
|
0.0133 | 0.0064 | |||||||
Hoek | |||||||||
rho | 0.0704 | 0.1287 | 0.0785 | 1 | |||||
|
0.6877 | 0.4611 | 0.6541 | ||||||
Creatinine |
|||||||||
rho | −0.0249 | −0.1967 | −0.0196 | 0.452 | 1 | ||||
|
0.8869 | 0.2575 | 0.911 | 0.0064 | |||||
Cystatin C |
|||||||||
rho | −0.0378 | 0.3552 | −0.0031 | 0.899 | 0.5299 | 1 | |||
|
0.8292 | 0.0363 | 0.986 | 0 | 0.0011 | ||||
Combined |
|||||||||
rho | 0.0084 | 0.0307 | 0.0401 | 0.7974 | 0.8418 | 0.8664 | 1 | ||
|
0.9618 | 0.861 | 0.8193 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.0547 | −0.13 | −0.0872 | −0.9985 | −0.4582 | −0.9032 | −0.8072 | 1 | |
|
0.7551 | 0.4567 | 0.6184 | 0 | 0.0056 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.0539 | −0.079 | −0.2187 | 0.2217 | 0.1269 | 0.0108 | 0.0239 | −0.1991 | 1 |
|
0.7583 | 0.6521 | 0.2068 | 0.2005 | 0.4676 | 0.9508 | 0.8918 | 0.2514 |
Stage 1 correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined |
Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.3645 | 1 | |||||||
|
0.0799 | ||||||||
Creatinine clearance | |||||||||
rho | −0.333 | −0.2031 | 1 | ||||||
|
0.1118 | 0.3411 | |||||||
Hoek | |||||||||
rho | 0.0961 | −0.3498 | 0.1409 | 1 | |||||
|
0.6551 | 0.0938 | 0.5114 | ||||||
Creatinine |
|||||||||
rho | 0.3765 | −0.7355 | 0.1748 | 0.3753 | 1 | ||||
|
0.0698 | 0 | 0.414 | 0.0707 | |||||
Cystatin C |
|||||||||
rho | 0.0722 | −0.445 | 0.1148 | 0.5932 | 0.507 | 1 | |||
|
0.7375 | 0.0293 | 0.5933 | 0.0022 | 0.0115 | ||||
Combined |
|||||||||
rho | 0.3183 | −0.7199 | 0.0791 | 0.4966 | 0.8522 | 0.8087 | 1 | ||
|
0.1296 | 0.0001 | 0.7132 | 0.0136 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.0453 | 0.5042 | −0.0571 | −0.7028 | −0.3969 | −0.8926 | −0.751 | 1 | |
|
0.8335 | 0.012 | 0.7911 | 0.0001 | 0.0548 | 0 | 0 | ||
Proteinuria | |||||||||
rho | 0.2517 | 0.1 | 0.2521 | −0.1154 | 0.1099 | −0.0882 | −0.0523 | 0.2501 | 1 |
|
0.2355 | 0.6422 | 0.2347 | 0.5912 | 0.6093 | 0.6821 | 0.8083 | 0.2384 |
Group 2 correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined |
Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.1853 | 1 | |||||||
|
0.184 | ||||||||
Creatinine clearance | |||||||||
rho | 0.2314 | −0.4016 | 1 | ||||||
|
0.0955 | 0.0029 | |||||||
Hoek | |||||||||
rho | 0.1178 | −0.6026 | 0.3886 | 1 | |||||
|
0.4008 | 0 | 0.004 | ||||||
Creatinine |
|||||||||
rho | 0.2172 | −0.8178 | 0.4104 | 0.737 | 1 | ||||
|
0.1182 | 0 | 0.0023 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.1633 | −0.51 | 0.3121 | 0.9496 | 0.7661 | 1 | |||
|
0.2427 | 0.0001 | 0.0229 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.1309 | −0.684 | 0.3815 | 0.8995 | 0.9182 | 0.9394 | 1 | ||
|
0.3501 | 0 | 0.0048 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.0603 | 0.5762 | −0.3461 | −0.9855 | −0.7272 | −0.9668 | −0.9111 | 1 | |
|
0.6713 | 0 | 0.012 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.1512 | 0.0199 | −0.1293 | −0.104 | −0.0046 | −0.1073 | −0.06 | 0.145 | 1 |
|
0.2848 | 0.8885 | 0.3608 | 0.4631 | 0.9742 | 0.4489 | 0.6727 | 0.3049 |
Group 3 correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined |
Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.4567 | 1 | |||||||
|
0 | ||||||||
Creatinine clearance | |||||||||
rho | 0.4212 | −0.6293 | 1 | ||||||
|
0 | 0 | |||||||
Hoek | |||||||||
rho | 0.4869 | −0.6661 | 0.6265 | 1 | |||||
|
0 | 0 | 0 | ||||||
Creatinine |
|||||||||
rho | 0.5033 | −0.909 | 0.7025 | 0.6755 | 1 | ||||
|
0 | 0 | 0 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.5073 | −0.641 | 0.6376 | 0.9734 | 0.7092 | 1 | |||
|
0 | 0 | 0 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.5317 | −0.8181 | 0.7324 | 0.9094 | 0.8994 | 0.9369 | 1 | ||
|
0 | 0 | 0 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.5045 | 0.688 | −0.6359 | −0.9864 | −0.7016 | −0.9873 | −0.9295 | 1 | |
|
0 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.3584 | 0.3975 | −0.3531 | −0.4105 | −0.3289 | −0.3881 | −0.3928 | 0.4341 | 1 |
|
0.0005 | 0.0001 | 0.0006 | 0.0001 | 0.0015 | 0.0002 | 0.0001 | 0 |
Group 4 correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine |
Cystatin C |
Combined |
Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.4418 | 1 | |||||||
|
0.001 | ||||||||
Creatinine clearance | |||||||||
rho | 0.5249 | −0.6193 | 1 | ||||||
|
0.001 | 0.0001 | |||||||
Hoek | |||||||||
rho | 0.618 | −0.8843 | 0.6417 | 1 | |||||
|
0.0001 | 0 | 0 | ||||||
Creatinine |
|||||||||
rho | 0.463 | −0.9433 | 0.6921 | 0.8519 | 1 | ||||
|
0.02 | 0 | 0 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.4525 | −0.8306 | 0.6759 | 0.9778 | 0.8486 | 1 | |||
|
0.003 | 0 | 0 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.5638 | −0.9105 | 0.7076 | 0.9356 | 0.956 | 0.9477 | 1 | ||
|
0.001 | 0 | 0 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.4998 | 0.8756 | −0.6531 | −0.9963 | −0.8499 | −0.9849 | −0.939 | 1 | |
|
0.001 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | −0.4995 | 0.4186 | −0.3834 | −0.487 | −0.3306 | −0.4612 | −0.39 | 0.4877 | 1 |
|
0.0003 | 0.0111 | 0.0001 | 0.0026 | 0.0489 | 0.0046 | 0.0187 | 0.0026 |
Group 5 correlations.
DTPA | Creatinine | Creatinine clearance | Hoek | Creatinine CKD-EPI | Cystatin C CKD-EPI | Combined CKD-EPI | Cystatin C | Proteinuria | |
---|---|---|---|---|---|---|---|---|---|
DTPA | |||||||||
rho | 1 | ||||||||
|
|||||||||
Creatinine | |||||||||
rho | −0.4491 | 1 | |||||||
|
0.0004 | ||||||||
Creatinine clearance | |||||||||
rho | 0.5414 | −0.7461 | 1 | ||||||
|
0 | 0 | |||||||
Hoek | |||||||||
rho | 0.4818 | −0.5612 | 0.6473 | 1 | |||||
|
0.0001 | 0 | 0 | ||||||
Creatinine |
|||||||||
rho | 0.4806 | −0.9656 | 0.7601 | 0.5904 | 1 | ||||
|
0.0001 | 0 | 0 | 0 | |||||
Cystatin C |
|||||||||
rho | 0.4683 | −0.4994 | 0.6202 | 0.9856 | 0.56 | 1 | |||
|
0.0002 | 0.0001 | 0 | 0 | 0 | ||||
Combined |
|||||||||
rho | 0.5288 | −0.8284 | 0.7759 | 0.8873 | 0.8815 | 0.8755 | 1 | ||
|
0 | 0 | 0 | 0 | 0 | 0 | |||
Cystatin C | |||||||||
rho | −0.4707 | 0.5456 | −0.6325 | −0.9974 | −0.5752 | −0.9886 | −0.8802 | 1 | |
|
0.0002 | 0 | 0 | 0 | 0 | 0 | 0 | ||
Proteinuria | |||||||||
rho | 0.2921 | 0.0209 | 0.2756 | 0.2272 | 0.1053 | 0.2564 | 0.2029 | 0.2269 | 1 |
|
0.0248 | 0.875 | 0.0346 | 0.0835 | 0.4273 | 0.05 | 0.1233 | 0.0839 |
With respect to proteinuria, it began to show significant correlations from stage 3 onwards (Tables
Bland-Altman plot between combined CKD-EPI and DTPA.
Bland-Altman plot between combined CKD-EPI and creatinine clearance.
Bland-Altman plot between combined CKD-EPI and CKD-EPI creatinine.
Bland-Altman plot between combined CKD-EPI and Hoek.
Bland-Altman plot between combined CKD-EPI and CKD-EPI cystatin.
Bland-Altman plot between combined CKD-EPI and proteinuria.
Briefly, in our previous recently published work, we have found that in the global 300-patient GFR evaluation, CKD-EPI and Hoek equations displayed the highest statistically significant correlations and the best lineal regressions with respect to
However, combined creatinine-cystatin C equations had not been included in that work. After the publication by Trimarchi et al. and Shlipak et al. in which GFR was assessed by several methods in a multicenter study with 1119 subjects employing urinary clearance of iothalamate as the gold standard, including creatinine, cystatin C or combined CKD-EPI formulas, showing that the combined CKD-EPI equation was superior to equations based on either creatinine or cystatin C markers alone, we decided to consider cystatin C and the combined CKD-EPI equations to our previous available data [
In our present study, creatinine clearance was the best method to assess GFR in the control group (Table
Besides, the main purpose of the development of newer equations should be focused on a higher precision of early detection of renal damage. Why is it important to focus on a correct GFR estimation at these early stages of CKD? It is important due to the large quantity of false negative CKD cases that are apparently being reported using the current methods [
When proteinuria was analyzed with respect to GFR ≤ 60 mL/min, it presented an inverse strong significant correlation with
With regard to the limitations of the present study, the cohort was not matched according to gender or age, and the different BMI varied significantly among the stages (Table
Kidney function assessment with combined CKD-EPI appears to be superior to other equations when
The authors declare that there is no conflict of interests regarding the publication of this paper.