Evaluation of renal function: use of clearance

2021-05-03 11:24 PM

The clearance of a substance represents the volume of plasma required to provide an equivalent amount of that substance is excreted in the urine per unit of time.

The degree to which various substances are leached from the plasma provides a useful means of evaluating the function of kidney substances to excrete.

By definition, the renal clearance from a substance is the volume of plasma that is completely filtered out of the substance by the kidney in a unit of time.

Although no substance can be completely filtered by the kidney in a single volume of plasma, the renal clearance provides a useful means of evaluating the renal function of secretion. Renal clearance can be used to assess renal blood flow, as well as the extent of glomerular filtration, tubular reabsorption, and tubular secretion.

To illustrate the principle of renal clearance, consider the following example: If plasma through the kidneys contain 1 mg of something per ml and 1 mg of that substance is excreted in the urine, then, 1 ml/min plasma clears the substance completely. Thus, the clearance of a substance represents the volume of plasma required to provide an equivalent amount of that substance that is excreted in the urine per unit of time.

 

Board. Use clearance to quantify kidney function

Cs, 's' clearance level; EPAH, rate of post PAH; ERPF, save efficient kidney compatibility Plasma flow; GFR, dialysis filtration rate; P, the concentration of a substance in plasma; PAH, para-amino hippuric acid; PPAH concentrations of PAH in the renal artery; RBF, renal blood flow; RPF, renal plasma flow; S, a substance; U, the concentration of a substance in urine; V, urine flow; VPAH, the PAH concentration in the renal vein.

We have the math formula:

Cs ×Ps = Us × V

where Cs is the clearance of substance s, Ps is the concentration of substance s in the blood plasma, Us is the concentration of substance s in the urine, and V is the urine flow.

Modifying the above formula, we can calculate the clearance of a substance by the formula:

Cs = (Us x V) / Ps

Therefore, the clearance of a substance can be calculated by the urinary output (Us × V) divided by the concentration of that substance in the blood plasma.

 

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