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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 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

Background Post-transplant diabetes mellitus (PTDM) beyond 12 months (late PTDM) is a severe complication after renal transplantation. Late PTDM develops mostly in subjects with prediabetes. Although exercise may have a potential role in preventing late PTDM, there is no previous data on the effect of exercise in patients with prediabetes. Material and methods we designed a 12-month exploratory study to test the capacity of exercise in reverting prediabetes in order to prevent late-PTDM. The outcome was the reversibility of prediabetes, assessed every 3 months with an oral glucose tolerance test (OGTT). The protocol included an incremental plan of aerobic and/or strength training as well as an active plan for promoting adherence (telephone calls, digital technology, and visits). Results the study included 27 prediabetic patients and was early interrupted due to efficacy. At the end of follow-up, 16 (60%) patients reverted to normal glucose levels at fasting and at 120 min after the OGTTs, two time higher than the 25–30% reversibility rate shown in a previous publication, p value

Background Diabetes is a risk factor for cancer in the general population. However, few data are available on the association between post-transplant diabetes mellitus (PTDM) and cancer after transplantation. Methods We analyzed this issue in a Spanish cohort of patients without diabetes before transplantation. PTDM was diagnosed with consensus criteria at 12 months after transplantation and 12 months before the diagnosis of cancer. The association between PTDM and cancer (overall and specific types) was evaluated with regression analysis. Results During a follow-up of 12 years (interquartile range 8–14), 85 cases of 603 developed cancer (829/100 000/year) and 164 (27%) PTDM. The most frequent cancers were renal cell cancer (RCC) n = 15, 146/cases/100 000/year), lung (n = 12, 117/cases/100 000/year), colon (n = 9, 88/cases/100 000/year) and prostate (n = 9, 88/cases/100 000/year). In logistic regression, PTDM was not associated with cancer. Eight of the 164 patients with PTDM (4.9%) vs 7 of the 439 without PTDM developed RCC (1.6%) (P = .027). In multivariate analysis, PTDM was independently associated with RCC [odds ratio (OR) 2.92, confidence interval (CI) 1.03–8.27], adjusting for smoking (OR 4.020, 95% CI 1.34–12.02) and other covariates. PTDM was not associated with other types of cancer. Conclusions Patients with PTDM must be considered a population at risk for RCC and accordingly, the subject of active surveillance.

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.

BackgroundReliable 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.MethodsWe 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 ResultsNinety-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.ConclusionThe 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.

Type 2 diabetes mellitus represents 30&ndash, 50% of the cases of end stage renal disease worldwide. Thus, a correct evaluation of renal function in patients with diabetes is crucial to prevent or ameliorate diabetes-associated kidney disease. The reliability of formulas to estimate renal function is still unclear, in particular, those new equations based on cystatin-C or the combination of creatinine and cystatin-C. We aimed to assess the error of the available formulas to estimate glomerular filtration rate in diabetic patients. We evaluated the error of creatinine and/or cystatin-C based formulas in reflecting real renal function over a wide range of glomerular filtration rate (from advanced chronic kidney disease to hyperfiltration). The error of estimated glomerular filtration rate by any equation was common and wide averaging 30% of real renal function, and larger in patients with measured glomerular filtration rate below 60 mL/min. This led to chronic kidney disease stages misclassification in about 30% of the individuals and failed to detect 25% of the cases with hyperfiltration. Cystatin-C based formulas did not outperform creatinine based equations, and the reliability of more modern algorithms proved to be as poor as older equations. Formulas failed in reflecting renal function in type 2 diabetes mellitus. Caution is needed with the use of these formulas in patients with diabetes, a population at high risk for kidney disease. Whenever possible, the use of a gold standard method to measure renal function is recommended.

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.

Background 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. Methods 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 Results 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. Conclusions 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.