Clearance Methods

The renal clearance of a compound is the volume of plasma from which that compound is completed removed by the kidneys per unit time (Pitts 1968). The material removed from the plasma is generally excreted in the urine. 

Clearance procedures can be conducted in all laboratory animal species anesthetized and conscious animal models may be used. Measurement of arterial pressure is advisable, especially in anesthetized preparations, to insure that renal perfusion pressure remains within the autoregulatory range (usually 80-120 mmHg). Vascular access ports can be helpful to provide continuous arterial access for pressure measurements (Mann et al. 1987). 

Carefully timed and complete collection of urine is critical to clearance studies. Urine can be collected directly from the ureters (anesthetized preparations) or via repeated catheterization of the urinary bladder in large animals (conscious preparations). Cannulated 

Tracers are administered intravenously to achieve near steady-state concentrations a priming dose loads the plasma and extracellular compartments, and subsequent infusion replaces renal losses. Once steady state plasma tracer levels are approached, a series of timed urine collections (clearance periods) are performed, with blood samples collected at the either the midpoint or beginning and end of the clearance periods. The urine and blood (plasma or serum) samples are analyzed for tracer(s) and the test compound. 

Inulin is measured colorimetrically, either by acid hydrolysis to generate a green product, or by a series of enzymatic reactions based on inulinase with subsequent reduction of NADH. HPLC methods are used for the remaining exogenous GFR tracers. PAH and TEA are measured colorimetrically (Newman and Price 1999). 

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Goetzova I, Skovranek I, Samanek M (1977) Muscle blood flow in children, measured by 133Xe clearance method. Cor Vasa, 19(2) 161-164. 

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 GFR can be measured most precisely using the 51Cr-EDTA clearance method, but for everyday practice the determination based on nomograms using serum creatinine values provides an adequately accurate estimate. It should be emphasized, however, that the myelotoxicity is also influenced by the general condition of the patient, especially by the extent of bone marrow reserve. Therefore, even when using an AUC-based administration scheme the seriousness of myelotoxicity cannot be accurately predicted. 

Finco et al. 2001) and for the rat using cystatin C (Tenstad et al. 1996). Either urine or plasma clearance methods can be used for the former. For the latter, plasma clearance was used to estimate GFR due to the fact that cystatin C is reabsorbed and degraded by the proximal tubule and does not appear in the urine. 

In situations when the GFR has been determined by accurate invasive clearance methods, either serum cystatin C or creatinine might be used to follow changes in GFR. However, as long as the precision of the methods for creatinine determination is higher than that of the methods for cystatin C determination, there are presently no valid reasons to use serum cystatin C for this purpose, particularly since creatinine determinations generally are cheaper than cystatin C determinations. 

Zahniser NR, Dickinson SD, Gerhardt GA. High-speed chronoam-perometric electrochemical measurements of dopamine clearance. Methods Enzymol. 1998 296 708-719. 

Radiopharmaceuticals that have been used include (1) Cr-(2) Tc-diethylenetriaminepentaacetic acid (DTPA), and (3) I-iothalamate. Cr-EDTA is preferred to 99mgamma camera imaging. T-iothalamate is no longer approved for intravascular use in some countries. GFR measurements may be based on either the urinary or plasma clearance of the marker. To ensure accuracy when measuring GFR using urinary clearance methods it is essential that (1) renal... 

Inuiin (sinistrin) continuous infusion urinary clearance method... 

Inuiin (sinistrin) single bolus plasma clearance method " Cr-EDTA... 

The rate of blood flow in the stomach and intestine of rabbits was assayed in vivo by the hydrogen clearance method. Compounds 1,28, and 29 increased the blood flow rate in the intestine by 15, 25, and 35%, respectively. In the stomach, however, 1 increased the rate by only 10%, and 28 decreased it (110). 

Since GFR cannot be measured directly, clearance methods involving substances that freely diffuse across the glomerulus and into Bowman s capsule without additional clearance by tubular secretion or reduction by reabsorption are required. Additionally, the substance should not be susceptible to metabolism within renal tissues and should not alter renal function. Given these conditions, the GFR is equivalent to the renal clearance of the solute marker ... 

This continuous infusion method can also be employed without urine collection, and plasma clearance is then calculated as CL = infusion rate/Css. Requirements of this method include steady-state plasma concentrations and accmate measmement of infusate concentrations. Plasma clearance can also be determined following a singledose intravenous injection with multiple samples of blood taken to estimate the area under the curve (AUCo oo)- Here clearance is calculated as CL = dose/AUC. These plasma clearance methods commonly yield clearance values 10% to 15% higher than urine collection methods. ... 

ERPF can also be measured using the radioisotopes I-orthoiodo-hippurate or Tc-mercaptoacetyltriglycine. One important advantage of this method is its ability to measure ERPF in total or for each kidney independently, as well as its ability to produce renal images. Russell and Dubovsky, using a single-injection technique, compared clearance methods with and without urine collection and showed similar results with each method. 

DowUng TC, Frye RF, Fraley DS, Matzke GR. Comparison of iotha-lamate clearance methods for measuring GFR. Pharmacotherapy 1999 19 943-950. 

Russell CD, Dubovsky EV. Comparison of single-injection multisample renal clearance methods with and without urine collection. J Nucl Med 1995 36 603-606. 

There is another broad problem of the greatest importance. When I was an interne in 1926, it was the accepted teaching that elevation of blood pressure was an attempt on the part of the body to force blood through thickened inelastic arteries and arterioles. In other words, thickening of the blood vessels with reduced lumens preceded the rise in blood pressure. To lower blood pressure was to court disaster, because then the tissues would not receive enough blood. For this reason the first research I ever did was to study this problem by means of Van Slyke s clearance method elaborated about 1928. 

Taves [164] has used renal clearance methods using fluorine-18 to obtain serum with a predicted 1.05X10" mol dm" fluoride and has shown the fluoride ion-selective electrode results to agree with those obtained by the fluorescence of a Morin—thorium complex. The electrode readings were taken on neutralised diffusates, a common method of isolating and concentrating fluoride but over which an alternative reverse extraction approach has recently been proposed [168]. 

As xanthine oxidase activity has been demonstrated to occur in the rat kidney but not in monkeys 5) the net secretion observed in rat proximal tubules could be due to cellular rather than to transtubular secretion. The influence of urate synthesis on urate excretion was studied by clearance methods in rats anesthetized with pentobarbital. The animals were infused with hypoxan-thine (0.5 ug/min)a metabolic precursor of urate, or allopurinol, (5 ug/min), a xanthine-oxidase inhibitor. 

A. A. Harper in Newcastle upon Tyne measured total blood flow through the stomachs of anesthetized cats by conventional methods and mucosal blood flow by multiplying the aminopyrine output into the lumen by its arteriovenous difference. He found a linear relation between H secretion and mucosal flow and no discontinuity when he extrapolated mucosal flow to zero H output. This implied that the clearance method is valid at a zero secretion rate. Three years later, gastroenter-... 

Jacobson ED, Eisenberg MM, Swan KG. Gastric blood flow in conscious animals, abstracted. Clin Res 13 536, 1965. The abstract was submitted December 1965, giving the latest date for the development of the aminopyrine clearance method, idem. Effects of histamine on gastric blood flow in conscious dogs. Gastroenterology 51 466-472, 1966. 

From 1996 till 2002 he researched landmine clearance methods and his web site is an internationally respected reference point for information on landmines. He was awarded with honorary membership of the Society of Counter Ordnance Technology in 2002 for his efforts, and was also elected a Eellow of the Institution of Engineers Australia. 

Perl, W., Heat and matter distribution in body tissues and the determination of tissue bloodflow by local clearance methods. J. Theor. Biol, 1962, 2 201-235. 

Pryor JA, Webber BA, Hodson BA, et al. Evaluation of the forced expiration technique as an adjunet to postural drainage in treatment of cystic fibrosis. BMJ 1979 2(6187) 417-418. American ThOTacic Society. Standards for the Diagnosis and Care of Patients with Chronic Obstructive Pulmonary Disease. Am J Respir Crit Care Med 1995 152(5 pt 2) S77-S121. Clarke SW, Pavia D. Lung mucus jnoduction and mucociliary clearance methods of assessment. Br J Clin Pharmacol 1980 9(6) 537-546. 

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