Inulin clearance test

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

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 following parameters may be determined inulin clearance (GFR), single nephron GFR, fractional delivery of water, sodium and potassium in proximal and distal tubules and in urine. All data are expressed as mean values SEM. Comparison of the effects of compounds to be tested with controls is performed by one way analysis of variance and by Student st-test for paired and unpaired data. 

The clearances of other compounds can be compared with inulin clearances to determine how the kidney functions in the elimination of the test compound. A clearance ratio is constructed by dividing the renal clearance of the test compound (X) by the renal clearance of inulin ... 

INULIN Inulin is a polymer of D-fructose molecules (fructofuranose), which are linked to each other in fi-2.1 bonds. There is a terminal glucose molecule. Inulin occurs as a reserve food instead of starch in plants, mainly within the family Asteraceae for example Inula helenium L., Asteraceae. In the form of a 10% aqueous solution inulin is used in tests of kidney function (like mannitol). Inulin is not absorbed or metabolised. Since there is no reabsorption in the tubules, the rate of excretion is a measure of the function of the glomerulus (inulin clearance). 

The results obtained by studying the effect of probenecid on the clearance of urate were consistent with the pyrazinamide test, indicating defective renal tubular reabsorption of urate. Administration of probenecid, which normally increases the urate clearance by two to five- fold (7), affected the uric acid clearance in the patient only slightly, increasing it from 55.3 ml/minute to 74.8 ml/minute. The ratio of the urate clearance to the inulin clearance increased from 65% to 84%. 

We were able to conduct three different studies of agents which interfere with renal transport of urate during continuous inulin infusions. The first such study (a pyrazinamide suppression test), is shown on the next slide. The data from these experiments will be shov/n as the ratio of urate clearance to inulin clearance. A ratio greater than 1.0 reflects tubular secretion while a lower ratio would suggest reabsorption. The time of day is on the horizontal axis labelled "hours". 

The starches, the most important vegetable reserve carbohydrate and polysaccharides from plant cell walls, are discussed in greater detail on the following page. Inulin, a fructose polymer, is used as a starch substitute in diabetics dietary products (see p.l60). In addition, it serves as a test substance for measuring renal clearance (see p.322). 

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