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A more accurate relationship between URR and Kt/V can be derived by single-pool, variable volume urea kinetic modeling. A simplified estimating equation also can be used. [2] This gives results that are quite similar to formal urea modeling as long as dialysis treatments of 2–6 hours in duration are given, and Kt/V is between 0.7 and 2.0.
K – dialyzer clearance of urea; t – dialysis time; V – volume of distribution of urea, approximately equal to patient's total body water; In the context of hemodialysis, Kt/V is a pseudo-dimensionless number; it is dependent on the pre- and post-dialysis concentration (see below).
It is complex and tedious to calculate, although web-based calculators are available to do this fairly easily. Many nephrologists have difficulty understanding it. Urea is not associated with toxicity. [4] Standardized Kt/V only models the clearance of urea and thus implicitly assumes the clearance of urea is comparable to other toxins.
The above equation makes clear the relationship between mass removal and clearance. It states that (with a constant mass generation) the concentration and clearance vary inversely with one another. If applied to creatinine (i.e. creatinine clearance ), it follows from the equation that if the serum creatinine doubles the clearance halves and ...
The above formula only applies for GFR calculation when it is equal to the clearance rate. The normal range of GFR, adjusted for body surface area , is 100–130 average 125 (mL/min)/(1.73 m 2 ) in men and 90–120 (mL/min)/(1.73 m 2 ) in women younger than the age of 40.
The renal clearance ratio or fractional excretion is a relative measure of the speed at which a constituent of urine passes through the kidneys. [ 1 ] [ 2 ] It is defined by following equation: c l e a r a n c e r a t i o o f X = C x C i n {\displaystyle clearance\ ratio\ of\ X={\frac {C_{x}}{C_{in}}}}
The glomerular filtration rate is the flow rate of filtered fluid through the kidney. The creatinine clearance rate (C Cr or CrCl) is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, [1] which can be blocked by ...
The normal clearance of urea is approximately 100 ml/min. A patient getting a conventional hemodialysis treatment, without remaining residual function, has a urea clearance of 10-15 ml/min. [ citation needed ]