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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 basic physiologic mechanisms of handling fluid and electrolytes by the nephron - filtration, secretion, reabsorption, and excretion - are labelled. Assessment of kidney function occurs in different ways, using the presence of symptoms and signs , as well as measurements using urine tests, blood tests, and medical imaging.
Extraction ratio is a measure in renal physiology, primarily used to calculate renal plasma flow in order to evaluate renal function. It measures the percentage of the compound entering the kidney that was excreted into the final urine. [1] Measured in concentration in blood plasma, it may thus be expressed as:
A sodium-related parameter is fractional sodium excretion, which is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is a useful parameter in acute kidney failure and oliguria , with a value below 1% indicating a prerenal disease and a value above 1% suggesting acute tubular necrosis or other kidney damage.
Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate [1] Although the strictest sense of the word excretion with respect to the urinary system is urination itself, renal clearance is also conventionally called excretion (for example, in the set term fractional excretion of sodium).
The fractional excretion of sodium (FE Na) is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is measured in terms of plasma and urine sodium , rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption .
In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) over the renal plasma flow (RPF). Filtration Fraction, FF = GFR/RPF, or =. The filtration fraction, therefore, represents the proportion of the fluid reaching the kidneys that passes into the renal tubules. It is normally about 20%.
Effective renal plasma flow (eRPF) is a measure used in renal physiology [1] to calculate renal plasma flow (RPF) and hence estimate renal function.. Because the extraction ratio of PAH is high, it has become commonplace to estimate the RPF by dividing the amount of PAH in the urine by the plasma PAH level, ignoring the level in renal venous blood.