If the percentage of creatinine that is secreted is ignored, then all of the filtered creatinine equal to the product of the GFR and the serum creatinine concentration [SCr] will be excreted equal to product of the urine creatinine concentration [UCr] and the urine flow rate or volume [V]. This formula is called the creatinine clearance and tends to exceed the true GFR by 10 to 20 percent or more depending upon the proportion of urinary creatinine that is derived from tubular secretion.
For more, see this article. Formulas like the Cockcroft-Gault Equation allow us to estimate GFR without using a hour urine collection by just using their sex, weight, age, and serum creatinine. Furthermore, the concordance analysis comparing creatinine clearance with inulin clearance showed a significant range of variation, which was also greater in the group of healthy patients. It is important to highlight that the concordance analysis used in our study, the one proposed by Bland and Altman, has been used ever more frequently in studies that compare two different methods for measuring clinical values, and has been especially used when the gold standard is to be replaced by another equally reliable but easier method.
Furthermore, correlation analysis only indicates the relationship between two variables, but not their concordance, since data that have a good correlation may have poor concordance, as was clearly shown in this study.
Although it is difficult to find different methods with exact concordance, it is necessary to know whether a new method varies in relation to the reference method, and once this is established, its clinical application can be assessed to determine if it can replace the old method. Irrespective of the method analysed, the limits of concordance were not sufficiently narrow to decide that one of the renal function tests studied could be used as a reference method.
This has greater importance in the context of clinical studies, when assessing a potential therapeutic strategy to try and slow down progression of renal damage. The equations can be used to provide approximate values of renal function; however, a method with less variability is necessary. Our results suggest that technetium clearance could be such method.
Due to the limitations mentioned above, we have proposed a panel of GFR markers, to make it easier to detect reduction of renal function at different stages and in different populations; however, this requires further study in the near future.
The different renal tests assessed estimated and measured showed an adequate correlation with the reference method; however, they all revealed a considerable lack of concordance, especially the two equations studied, which was more evident in the healthy population.
Technetium clearance showed less discrepancy, in comparison with inulin clearance, although none of the tests analysed is capable of substituting this test. Figure 1. Concordance between inulin clearance and Tc clearance.
Figure 2. Concordance between inulin clearance and creatinine clearance. Figure 3. Concordance between inulin clearance and the Cockroft formula.
Figure 4. Concordance between inulin clearance and the Levey formula. Table 1. Home Articles in press Archive. ISSN: Previous article Next article. May Pages More article options. DOI: Comparison of four methods for measuring glomerular filtration rate by inulin clearance in healthy individuals and patients with renal failure.
Download PDF. Ignacio Ch?? This item has received. Article information. Show more Show less. The measurement of glomerular filtration rate determined via different methods shows a wide range of variation when compared with inulin clearance, which should be considered in daily clinical practice during the evaluation of renal function.
Tc99m-DTPA clearance. Creatinine clearance. Cockcroft formula. Inulin clearance. Glomerular filtration rate. Palabras clave:. Full Text. Philadelphia, Pa: Saunders; ; Renal function and testing of function. Oxford Textbook of Clinical Nephrology Vol. Ann Intern Med ; Serum creatinine as an index of renal function: New insights into old concepts.
Clin Chem ; ?? Application of newer clearance techniques for the determination of glomerular filtration rate. Curr Opin Nephrol Hypertens ; Nephron ; Estudios sobre la medici?? The Cockcroft-Gault equation estimates creatinine clearance and incorporates weight into the equation. As a result, an individual patient may have very different renal function estimates, depending on the equation used.
We now highlight these differences and discuss the impact on routine clinical care for anticoagulation to prevent embolization in atrial fibrillation.
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