Inulin clearance is now accepted as the standard for estimation of the GFR.
The clearance of inulin and some other compounds is not altered by raising its plasma concentration, because the amount of urine completely cleared of the agent remains the same.
The clearance of creatinine was used as a measure of renal function before inulin was discovered; because this substance is found naturally in plasma, creatinine clearance is still widely used as an approximate measure of the GFR.
The first substance identified to be excreted in this way was the polysaccharide inulin (molecular weight about 5,000), which is extracted from the roots of dahlias.
Although inulin is not naturally found in human plasma it is nontoxic and can be injected or infused into the bloodstream.
Other homopolysaccharides include pentosans (composed of arabinose or xylose) from woods, nuts, and other plant products; and fructans (levans) composed of fructose, such as inulin from roots and tubers of the Jerusalem artichoke and dahlia.
Difficulties involved in carrying out the inulin clearance procedure, however, render creatinine clearance the more practical clinical measurement with which to assess renal function.
Since the discovery of inulin, researchers have identified a small number of other substances that are excreted by the kidney in a similar fashion and that have similar clearance values.
Creatinine clearance is a slightly less accurate measure of the glomerular filtration rate than inulin clearance because, unlike inulin, a small amount of creatinine is reabsorbed by the kidney and is not excreted in the urine, thereby being lost to measurement.
To boost fiber, the food industry added lots of a polysaccharide called inulin to hundreds of products, but that's just one kind (often derived from the chicory-plant root) and so may only favor a limited number of microbes.
Chicory contains a type of soluble fiber called inulin, which some studies suggest may have a positive effect on blood sugar levels.
