Creatinine, ultrafiltration

EN35 Hardeman, D. and Backer, E.T. (1991). Ultrafiltration of serum to eliminate bilirubin interference in the kinetic Jaffe determination of creatinine. Clin. Chem. 37, 20KU2011. 

The assessment of adequacy of dialysis treatment for individual patients in the clinical setting includes consideration of the patient s well-being, cardiovascular risk, nutritional status, and degree of achievable ultrafiltration. It also includes estimates of a number of laboratory parameters— such as hemoglobin, phosphate, and albumin— and clearance of the small solutes urea and creatinine. During die following discussion, the term adequacy will refer to small solute clearances obtained from both dialysis and residual renal function (RRF), For practical reasons, HD adequacy is calculated using urea as the small solute. 

This syndrome of functional ARE is very common in individuals with CHE who receive an ACEI in an attempt to improve left ventricular function. The decline in efferent arteriolar resistance resulting from the inhibition of angiotensin II occurs rapidly. Therefore, if the dose of the ACEI is increased too rapidly, there will be a decline in glomerular ultrafiltrate production with a concomitant rise in the serum creatinine, leading to functional ARE. If the increase in the serum creatinine is not too severe (usually <1 mg/dL) the medication can be continued. Renal function should gradually improve as renal parenchymal perfusion pressure increases with improvement in left ventricular function. 

Blood plasma and ultrafiltrate concentrations of urea and creatinine have been studied with subcutaneous ultrafiltrate probes in diabetic dogs. The dogs had varying degrees of kidney complications secondary to the diabetes. 

In hemodialysis, low molecular metabolic waste such as urea, creatinine, and other toxic substances (solutes up to 6000 mol wt) are removed from the blood of uremia patients by diffusive transport, which is driven by a concentration gradient of blood solutes being dialyzed against a physiological solution. A complimentary process is hemofiltration, in which solutes up to 20,000 mol wt are removed via an ultrafiltration membrane, the transport being caused by a convective transmembrane flux generated by mild hydraulic pressure differences across the membrane. 

Hollow fiber membranes (HFMs) formed via phase inversion methods exhibit specific physicochemical characteristics and generally favorable surface and mechanical properties. Due to these properties the HFMs can be used in diverse applications including ultrafiltration, gas separation, dialysis, cell culture, bioreactors, and tissue engineering. Most artificial kidneys are based on hollow fiber membranes. Blood is circulated through the center of the fiber, while isotonic saline, the dialysate, is pumped countercurrently around the outside of the fibers. Urea, creatinine, and other low-molecular weight metabolites in the blood diffuse across the fiber wall and are removed with the saline solution. 

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