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Measuring residual renal function in dialysis patients with glomerular filtration rate close to zero

 

Krista Dybtved Kjaergaard

Summary

The mortality in dialysis patients is around 20% per year. However, recent researchhas revealed that preservation of residual renal function (RRF) in dialysis patients,even at a very low range, is associated with decreased morbidity and mortality.This knowledge has shed new light on the importance of preserving RRF. However,strategies on preservation of RRF are mainly based on observational studies. Forclinical randomized studies of strategies to preserve RRF, validated methods toestimate glomerular filtration rate (GFR) in dialysis patients are needed.Measurement of GFR as tracer clearance is the gold standard used in clinicalpractice in patients with normal and decreased kidney function, whereas the use ofthis method has been scarce in dialysis patients.We investigated 12 hemodialysis (HD) patients and 12 peritoneal dialysis (PD)patients twice. At both visits, clearance of the tracer 51Cr-EDTA was measured inplasma, urine and for PD patients also in the dialysate together with clearance ofcreatinine and urea, and serum concentrations of Cystatin C.We found that plasma clearance of 51Cr-EDTA (with dialysate clearance subtractedin PD patients) was the most reproducible method, but the measured clearanceswere around a third larger than urinary 51Cr-EDTA clearances, and the method wascomplex and labor-intensive. Among endogenous markers, U-Cl(crea-urea) wasprobably closest to the true GFR in both populations.Two equations recently introduced in the literature for estimation of GFR fromserum Cystatin C were evaluated. Both equations seemed skewed in comparisonwith the other methods investigated.For follow-up studies, plasma clearance of 51Cr-EDTA in highly standardized settingsmay be useful due to a good reproducibility, whereas averaged creatinine and urea clearance is more appropriate for clinical practice. Further studies of Cystatin Cbasedequations are needed before this method could be recommended.