Obesity is an established risk factor for renal disease and for disease progression. Therefore, an accurate determination of renal function is necessary in this population. Renal function is ...currently evaluated by estimated glomerular filtration rate (GFR) by formulas, a procedure with a proven high variability. Moreover, the adjustment of GFR by body surface area (BSA) confounds the evaluation of renal function. However, the error of using estimated GFR adjusted by BSA has not been properly evaluated in overweight and obese subjects.
We evaluated the error of 56 creatinine- and/or cystatin-C-based equations and the adjustment of GFR by BSA in 944 subjects with overweight or obesity with or without chronic kidney disease (CKD). The error between estimated (eGFR) and measured GFR (mGFR) was evaluated with statistics of agreement: the total deviation index (TDI), the concordance correlation coefficient (CCC) and the coverage probability (cp).
The error of eGFR by any equation was common and wide: TDI averaged 55%, meaning that 90% of estimations ranged from -55 to 55% of mGFR. CCC and cp averaged 0.8 and 26, respectively. This error was comparable between creatinine and cystatin-C-based formulas both in obese or overweight subjects. The error of eGFR was larger in formulas that included weight or height. The adjustment of mGFR or eGFR led to a relevant underestimation of renal function, reaching at least 10 mL/min in 25% of the cases.
In overweight and obese patients, formulas failed in reflecting real renal function. In addition, the adjustment for BSA led to a relevant underestimation of GFR. Both errors may have important clinical consequences. Thus, whenever possible, the use of a gold standard method to measure renal function is recommended. Moreover, the sense of indexing for BSA should be re-considered and probably abandoned.
Background & Aims
In cirrhosis, the reliability of formulas that estimate renal function, either those specifically developed in this population or the classic equations, has not been properly ...quantified. We studied the agreement between estimated (eGFR) and measured glomerular filtration rate (mGFR) in cirrhosis.
Methods
Renal function was estimated with 56 formulas including specific equations: Glomerular Filtration Rate Assessment in Liver Disease (GRAIL), Royal Free Hospital Cirrhosis (RFHC) and Mindikoglu‐eGFR, and measured with a gold standard procedure; plasma clearance of iohexol using dried blood spots sampling in a group of cirrhotics. The agreement eGFR‐mGFR was evaluated with specific tests: total deviation index (TDI), concordance correlation coefficient (CCC) and coverage probability (CP). We defined acceptable agreement as values: TDI < 10%, CCC ≥ 0.9 and CP > 90%.
Results
A total of 146 patients (age 65 ± 9 years, 81% male) were evaluated; 61 (42%) Child A, 67 (46%) Child B and 18 (12%) Child C. Median MELD‐Na was 14 (9‐15). The agreement between eGFR and mGFR was poor: TDI averaged was of 73% (90% of the estimations ranged from ±73% of mGFR); CCC averaged was 0.7 indicating low concordance and CP averaged 22% indicating that 78% of the estimations have an error > 10%. Specific formulas showed also poor agreement: TDI was 82%, 70% and 37% for the GRAIL, RFHC and Mindikoglu equations, respectively.
Conclusions
Overall, formulas poorly estimated renal function in cirrhotic patients. Specific formulas designed for cirrhosis did not outperform classic equations. eGFR must be considered with caution in cirrhotic patients.
The evaluation of renal function changes over time is crucial in day-to-day renal transplant care, and the slope of renal function is a major outcome in clinical trials. Little is known about the ...reliability of estimated glomerular filtration rate (eGFR) in reflecting real glomerular filtration rate (GFR) changes.
We analyzed the variability of eGFR slope by 63 equations in estimating measured GFR (mGFR) changes in 110 renal transplant patients. The agreement between eGFR and mGFR slopes was evaluated by the concordance correlation coefficient and the limits of agreement. Patients were grouped based on mGFR slope in rapid GFR loss: faster than -3 mL/min/y; stable renal function: -3 to +3 mL/min/y; and improvement in GFR: higher than +3 mL/min/y.
Concordance correlation coefficient averaged 0.36 and limits of agreement ±10 mL/min/y, indicating very poor agreement between eGFR and mGFR slopes. The eGFR slope classified patients into the same group of mGFR slope only in 25% of the cases. In about two-thirds of patients, the eGFR slope was either markedly faster or slower than the mGFR slope. In half of these cases, the discrepancy between mGFR and eGFR slopes was ≥50%.
Formulas are neither accurate nor precise in reflecting real GFR decline in renal transplant patients, making them unreliable for clinical practice and trials.
The error of estimated GFR in predialysis care Escamilla-Cabrera, Beatriz; Luis-Lima, Sergio; Gallego-Valcarce, Eduardo ...
Scientific reports,
03/2024, Letnik:
14, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The error of estimated glomerular filtration rate (eGFR) and its consequences in predialysis are unknown. In this prospective multicentre study, 315 predialysis patients underwent measured GFR (mGFR) ...by the clearance of iohexol and eGFR by 52 formulas. Agreement between eGFR and mGFR was evaluated by concordance correlation coefficient (CCC), total deviation index (TDI) and coverage probability (CP). In a sub-analysis we assessed the impact of eGFR error on decision-making as (i) initiating dialysis, (ii) preparation for renal replacement therapy (RRT) and (iii) continuing clinical follow-up. For this sub-analysis, patients who started RRT due to clinical indications (uremia, fluid overload, etc.) were excluded. eGFR had scarce precision and accuracy in reflecting mGFR (average CCC 0.6, TDI 70% and cp 22%) both in creatinine- and cystatin-based formulas. Variations -larger than 10 ml/min- between mGFR and eGFR were frequent. The error of formulas would have suggested (a) premature preparation for RTT in 14% of stable patients evaluated by mGFR; (b) to continue clinical follow-up in 59% of subjects with indication for RTT preparation due to low GFRm and (c) to delay dialysis in all asymptomatic patients (n = 6) in whom RRT was indicated based on very low mGFR. The error of formulas in predialysis was frequent and large and may have consequences in clinical care.
Autosomal polycystic kidney disease (ADPKD) is the most common genetic form of kidney failure, reflecting unmet needs in management. Prescription of the only approved treatment (tolvaptan) is limited ...to persons with rapidly progressing ADPKD. Rapid progression may be diagnosed by assessing glomerular filtration rate (GFR) decline, usually estimated (eGFR) from equations based on serum creatinine (eGFRcr) or cystatin-C (eGFRcys). We have assessed the concordance between eGFR decline and identification of rapid progression (rapid eGFR loss), and measured GFR (mGFR) declines (rapid mGFR loss) using iohexol clearance in 140 adults with ADPKD with ≥3 mGFR and eGFRcr assessments, of which 97 also had eGFRcys assessments. The agreement between mGFR and eGFR decline was poor: mean concordance correlation coefficients (CCCs) between the method declines were low (0.661, range 0.628 to 0.713), and Bland and Altman limits of agreement between eGFR and mGFR declines were wide. CCC was lower for eGFRcys. From a practical point of view, creatinine-based formulas failed to detect rapid mGFR loss (-3 mL/min/y or faster) in around 37% of the cases. Moreover, formulas falsely indicated around 40% of the cases with moderate or stable decline as rapid progressors. The reliability of formulas in detecting real mGFR decline was lower in the non-rapid-progressors group with respect to that in rapid-progressor patients. The performance of eGFRcys and eGFRcr-cys equations was even worse. In conclusion, eGFR decline may misrepresent mGFR decline in ADPKD in a significant percentage of patients, potentially misclassifying them as progressors or non-progressors and impacting decisions of initiation of tolvaptan therapy.
Renal function can be estimated with formulas, which are inaccurate, or measured with gold standard methods, which are reliable but unpractical. We propose to simplify the plasma clearance of ...iohexol, a gold standard method to measure renal function, by dried blood spot (DBS) testing.
We compared glomerular filtration rate (GFR) values assessed by DBS and the reference plasma analysis technique. We tested in vitro the agreement between non-volumetric and volumetric DBS with the reference technique. Then, we performed a clinical validation in vivo between volumetric DBS and plasma analysis in 203 patients. The agreement was evaluated with the concordance correlation coefficient (CCC), the total deviation index (TDI) and the coverage probability. We defined acceptable agreement as a TDI <10%.
In the in vitro studies, the non-volumetric DBS showed moderate agreement, TDI = 26.0%, while the volumetric method showed better but insufficient agreement, TDI = 13.0%, with the reference method in plasma. The non-volumetric DBS was rejected. To improve the agreement of the volumetric DBS, iopamidol was used as an internal standard. This method showed acceptable agreement, TDI = 9.0% with the analysis in plasma, and was selected as the definitive DBS method. In the in vivo studies, the agreement between the final DBS method and the reference technique was acceptable: TDI = 9.5%. This indicates that 90% of the GFR values ranged from -9.5% to + 9.5% compared with the reference method.
We simplified the plasma clearance of iohexol using DBS without losing accuracy and precision with respect to the reference technique. This may facilitate the use of a reliable determination of renal function to the medical community.
Abstract
Background
Chronic kidney disease (CKD) affects 10–13% of the population worldwide. CKD classification stratifies patients in five stages of risk for progressive renal disease based on ...estimated glomerular filtration rate (eGFR) by formulas and albuminuria. However, the reliability of formulas to reflect real renal function is a matter of debate. The effect of the error of formulas in the CKD classification is unclear, particularly for cystatin C–based equations.
Methods
We evaluated the reliability of a large number of cystatin C and/or creatinine-based formulas in the definition of the stages of CKD in 882 subjects with different clinical situations over a wide range of glomerular filtration rates (GFRs) (4.2–173.7 mL/min).
Results
Misclassification was a constant for all 61 formulas evaluated and averaged 50% for creatinine-based and 35% for cystatin C–based equations. Most of the cases were misclassified as one stage higher or lower. However, in 10% of the subjects, one stage was skipped and patients were classified two stages above or below their real stage. No clinically relevant improvement was observed with cystatin C–based formulas compared with those based on creatinine.
Conclusions
The error in the classification of CKD stages by formulas was extremely common. Our study questions the reliability of both cystatin C and creatinine-based formulas to correctly classify CKD stages. Thus the correct classification of CKD stages based on estimated GFR is a matter of chance. This is a strong limitation in evaluating the severity of renal disease, the risk for progression and the evolution of renal dysfunction over time.
Formulas do not estimate renal function with acceptable precision and accuracy.
We compared 51 creatinine-based and/or cystatin c-based formulas with a gold standard (iohexol plasma clearance) in 193 ...renal transplant recipients using concordance correlation coefficient, total deviation index, coverage probability and the error in chronic kidney disease (CKD) stage classification.
No formula showed a concordance correlation coefficient greater than 0.90 (average for creatinine-based formulas: ∼0.70 and for cystatin c-based formulas: ∼0.85). A wide total deviation index was observed: approximately 70% (creatinine-based) and approximately 50% (cystatin c-based), indicating that 90% of the estimations showed bounds of error of ±70% or ±50%, respectively, compared with the gold standard. No formula included 90% of the estimations within a coverage probability of ±10%. Half the CKD stages classified by creatinine-based formulas were incorrect, mainly due to overestimation of renal function. One of 3 CKD stages diagnosed by cystatin c-based formulas was incorrect, with both overestimation and underestimation. Overall, the formulas showed very low precision and accuracy and a high degree of error in reflecting real renal function.
In conclusion, formulas do not properly reflect renal function in kidney transplantation, which makes their use in clinical practice unreliable. Moreover, their use in clinical trials should be avoided.
Background
Autosomal dominant polycystic kidney disease (ADPKD) causes about 10% of cases of end stage renal disease. Disease progression rate is heterogeneous. Tolvaptan is presently the only ...specific therapeutic option to slow kidney function decline in adults at risk of rapidly progressing ADPKD with chronic kidney disease (CKD) stages 1–4. Thus, a reliable evaluation of kidney function in patients with ADPKD is needed.
Methods
We evaluated the agreement between measured (mGFR) and estimated glomerular filtration rate (eGFR) by 61 formulas based on creatinine and/or cystatin-C (eGFR) in 226 ADPKD patients with diverse GFR values, from predialysis to glomerular hyperfiltration. Also, we evaluated whether incorrect categorization of CKD using eGFR may interfere with the indication and/or reimbursement of Tolvaptan treatment.
Results
No formula showed acceptable agreement with mGFR. Total Deviation Index averaged about 50% for eGFR based on creatinine and/or cystatin-C, indicating that 90% of the estimations of GFR showed bounds of error of 50% when compared with mGFR. In 1 out of 4 cases with mGFR < 30 ml/min, eGFR provided estimations above this threshold. Also, in half of the cases with mGFR between 30 and 40 ml/min, formulas estimated values < 30 ml/min.
Conclusions
The evaluation of renal function with formulas in ADPKD patients is unreliable. Extreme deviation from real renal function is quite frequent. The consequences of this error deserve attention, especially in rapid progressors who may benefit from starting treatment with tolvaptan and in whom specific GFR thresholds are needed for the indication or reimbursement. Whenever possible, mGFR is recommended.
Graphic abstract
Abstract
Background
Reliable determination of glomerular filtration rate (GFR) is crucial in the evaluation of living kidney donors. Although some guidelines recommend the use of measured GFR (mGFR), ...many centres still rely on estimated GFR (eGFR) obtained through equations or 24-h creatinine clearance. However, eGFR is neither accurate nor precise in reflecting real renal function. We analysed the impact of eGFR errors on evaluation and decision making regarding potential donors.
Methods
We evaluated 103 consecutive living donors who underwent mGFR via iohexol plasma clearance and eGFR by 51 creatinine- and/or cystatin C–based equations. The cut-off for living donation in our centre is GFR > 80 mL/min for donors >35 years of age or 90 mL/min for those <35 years of age. We analysed the misclassification of donors based on the cut-off for donation-based eGFR.
Results
Ninety-three subjects (90.3%) had mGFR values above (donors) and 10 9.7% (95% confidence interval 5.4–17) below (non-donors) the cut-off. In non-donors, most of the equations gave eGFR values above the cut-off, so donation would have been allowed based on eGFR. All non-donors were female with reduced weight, height and body surface. In donors, up to 32 cases showed eGFR below the cut-off, while mGFR was actually higher. Therefore an important number of donors would not have donated based on eGFR alone.
Conclusion
The misclassification of donors around the cut-off for donation is very common with eGFR, making eGFR unreliable for the evaluation of living kidney donors. Whenever possible, mGFR should be implemented in this setting.
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