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Can be applied to patients with residual renal function; it is possible to demonstrate that C o is a function of the residual kidney function and the "cleaning" provided by dialysis. The model can be applied to substances other than urea, if the clearance, K , and generation rate of the substance, m ˙ {\displaystyle {\dot {m}}} , are known.
Blood tests are also used to assess kidney function. These include tests that are intended to directly measure the function of the kidneys, as well as tests that assess the function of the kidneys by looking for evidence of problems associated with abnormal function. One of the measures of kidney function is the glomerular filtration rate (GFR).
Diagram showing the basic physiologic mechanisms of the kidney. 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: =
where C is the concentration [mol/m 3]; t is the time [s]; K is the clearance [m 3 /s]; V is the volume of distribution [m 3]; From the above definitions it follows that is the first derivative of concentration with respect to time, i.e. the change in concentration with time.
A simple means of estimating renal function is to measure pH, blood urea nitrogen, creatinine, and basic electrolytes (including sodium, potassium, chloride, and bicarbonate). As the kidney is the most important organ in controlling these values, any derangement in these values could suggest renal impairment.
This is the numerator in the equation. The denominator is the total amount of sodium filtered by the kidneys. This is calculated by multiplying the plasma sodium concentration by the glomerular filtration rate (GFR) calculated using creatinine filtration. The flow rates then cancel out, simplifying to the standard equation: [1]
Levey is known for developing the most widely used equations to estimate GFR (renal function) globally.He pioneered work with the MDRD Study Equation, [1] led the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), which pooled measured kidney function CKD data from studies all over the world to develop equations to estimate kidney function from serum creatinine, cystatin C, and ...
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: