The (99m)Tc-DTPA urinary clearance method may be preferable to the plasma disappearance method for assessing glomerular filtration rate in diabetic nephropathy

Measured Glomerular Filtration Rate: The Query for a Workable Golden Standard Technique

Inulin clearance has, for a long time, been considered as the reference method to determine measured glomerular filtration rates (mGFRs). However, given the known limitations of the standard marker, serum creatinine, and of inulin itself, and the frequent need for accurate GFR estimations, several other non-radioactive (iohexol and iothalamate) and radioactive (51Cr-EDTA, 99mTc-DTPA, 125I iothalamate) exogenous mGFR filtration markers are nowadays considered the most accurate options to evaluate GFR. The availability of 51Cr-EDTA is limited, and all methods using radioactive tracers necessitate specific safety precautions. Serum- or plasma-based certified reference materials for iohexol and iothalamate and evidence-based protocols to accurately and robustly measure GFR (plasma vs. urinary clearance, single-sample vs. multiple-sample strategy, effect of sampling time delay) are lacking. This leads to substantial variation in reported mGFR results across studies and questions the scientific reliability of the alternative mGFR methods as the gold standard to evaluate kidney function. On top of the scientific discussion, regulatory issues are further narrowing the clinical use of mGFR methods. Therefore, this review is a call for standardization of mGFR in terms of three aspects: the marker, the analytical method to assess concentrations of that marker, and the procedure to determine GFR in practice. Moreover, there is also a need for an endogenous filtration marker or a panel of filtration markers from a single blood draw that would allow estimation of GFR as accurately as mGFR, and without the need for application of anthropometric, clinical, and demographic characteristics.

Preservation of residual kidney function in hemodialysis patients: reviving an old concept

Residual kidney function (RKF) may confer a variety of benefits to patients on maintenance dialysis. RKF provides continuous clearance of middle molecules and protein-bound solutes. Whereas the definition of RKF varies across studies, interdialytic urine volume may emerge as a pragmatic alternative to more cumbersome calculations. RKF preservation is associated with better patient outcomes including survival and quality of life and is a clinical parameter and research focus in peritoneal dialysis. We propose the following practical considerations to preserve RKF, especially in newly transitioned (incident) hemodialysis patients: (1) periodic monitoring of RKF in hemodialysis patients through urine volume and including residual urea clearance with dialysis adequacy and outcome markers such as anemia, fluid gains, minerals and electrolytes, nutritional, status and quality of life; (2) avoidance of nephrotoxic agents such as radiocontrast dye, nonsteroidal anti-inflammatory drugs, and aminoglycosides; (3) more rigorous hypertension control and minimizing intradialytic hypotensive episodes; (4) individualizing the initial dialysis prescription with consideration of an incremental/infrequent approach to hemodialysis initiation (e.g., twice weekly) or peritoneal dialysis; and (5) considering a lower protein diet, especially on nondialysis days. Because RKF appears to be associated with better patient outcomes, it requires more clinical and research focus in the care of hemodialysis and peritoneal dialysis patients.