Glomerular filtration rate inulin clearance

See also /7-aminohippuric acid, creatinine, glomerular filtration rate, inulin clearance test, renal plasma flow, tubular secretory capacity... 

From a scientific point of view, glomerular filtration rate (inulin or creatinine clearance) is the best global estimate of renal function. Other parameters of interest include, but are not limited to ... 

The answer of 1500 litres a day exceeds the renal plasma flow (typically 900 litres a day). The reason is that the renal tubular cells are themselves a source of metabolically derived ammonia which diffuses into the tubular fluid and combines with hydrogen ions there to give ammonium ions. The renal clearance for ammonium therefore bears no relation to renal plasma flow. Clearance values of other chemicals are only indicative of such parameters as renal plasma flow (PAH) or glomerular filtration rate (inulin) for chemicals for which there is no source or sink in the kidneys themselves. 

Inulin is a plant polysaccharide which, when infused intravenously, is filtered at the glomerulus and excreted in the urine without reabsorption or secretion by the renal tubules. Estimation of its clearance is therefore a measure of the glomerular filtration rate. Inulin can be measured by the red colour it gives with resorcinol, following hydrolysis. 

Explain how plasma clearance of inulin is used to determine glomerular filtration rate... 

The marker remains in the plasma without binding to proteins, and the filtrate is neither reabsorbed nor secreted by the renal tubule. Clearance rate of the marker from plasma equals the glomerular filtration rate (GFR). The polysaccharide, inulin, typifies this class of markers. 

Inulin is used in an important test for renal failure called the inulin clearance method (Gretz et al., 1993 Chiu, 1994). As inulin is neither secreted nor reabsorbed in the kidney, it can be administered by injection to measure glomerular filtration rate. The relative amounts of inulin in the plasma and urine give an indication of renal function. 

The determination of renal function in anesthetized animals provides specific information on the effects of chemicals on glomerular filtration rate and renal blood flow. In addition, the ability of the kidney to reabsorb or secrete electrolytes may be determined by fractional clearance of Na+, K+, HCO3, Cl, and so on. Fractional clearance involves comparison of electrolyte clearance to the clearance of a substance such as inulin, which is removed from plasma by glomerular filtration. Thus, fractional clearance takes glomerular filtration rate into account, allowing comparisons of electrolyte transport between treated and control animals even if renal hemodynamics have changed. Nephron function may be assessed by free water clearance, representing the ability of the kidney to remove almost all Na+ from urine. 

Formal measures of glomerular filtration rate (GFR), using intravenous inulin or radio-iodinated sodium iothalamate, will not have been performed on most patients with relative renal failure in ordinary clinical practice. Of several alternatives in adults, creatinine (Cr) clearance (CrCL) is probably the most commonly employed, and uses the familiar formula ... 

Arant BS Jr. Developmental patterns of renal functional maturation compared in the human neonate. J Pediatr 1978 92 705-712. van den Anker, de Groot R, Broerse HM, et al. Assessment of glomerular filtration rate in preterm infants by serum creatinine Comparison with inulin clearance. Pediatrics 1995 96 1156-1158. 

After 20-30 min for equilibration, perfusate samples are collected to coincide with the start of urine collections at 5 to 15 min intervals. The urine volume depends on both perfusion pressure and oncotic pressure [102]. Perfusion pressure and flow are monitored continuously. Renal function is assessed from renal vascular resistance, urine flow, the ratio of l C-inulin in urine to plasma (U/Pinulin), glomerular filtration rate (GFR as inulin clearance UV/P) and the fractional excretion of sodium (FEjvja) potassium (FEj ). Inulin measurement can also be performed chemically. In some situations GFR is misleading as an index of "good function" in this model. For example, in the absence of an oncotic agent, a "reasonable" GFR is over 1 ml/ g/ min, however U/Pinulin is rarely more than 2, FENa is over 0.1 and histological examination shows extensive proximal necrosis within 20-40 min of initiating perfusion. It appears that in this situation the massive... 

Gaspan F, Amuchastegui CS, Guerini E, Perico N, Mosconi L, Ruggenenti P, Remuzzi G. Plasma clearance of nonradioactive iohexol as an alternative to renal clearance of inulin for measurement of glomerular filtration rate in humans. J Am Soc Nephrol 1993 4 315. 

Although inulin clearance is generally accepted as the most accurate method for the estimation of glomerular filtration rate, which is approximately 125mLmin in healthy indivi-... 

Qi Z, Whitt I, Mehta A, Jin J, Zhao M, Harris RC, Fogo AB, Breyer MD. (2004) Serial determination of glomerular filtration rate in conscious mice using FITC-inulin clearance. Am J Physiol Ren Physiol. 286 F590-F596. 

Jung K, Henke W, Schulze BD, Sydow K, Precht K, and S Klotzek (1992). Practical approach for determining glomerular filtration rate by single-injection inulin clearance. Clinical Chemistry 38 403 07. 

All experiments were performed in well-hydrated subjects after an overnight fast. Glomerular filtration rate (GFR) was measured using Inulin or lothalamate 1125 clearance (6), the latter being especially useful in the presence of high blood and urine levels of glucose. The GFR was always expressed as ml/min/1.73 M2... 

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