Reciprocal serum creatinine concentration and chronic kidney disease
- Anthony Bleyer, MD, MS
Anthony Bleyer, MD, MS
- Professor of Internal Medicine/Nephrology
- Wake Forest University School of Medicine
- Section Editors
- Gary C Curhan, MD, ScD
Gary C Curhan, MD, ScD
- Section Editor — Chronic Kidney Disease
- Professor of Medicine
- Harvard Medical School
- Richard H Sterns, MD
Richard H Sterns, MD
- Editor-in-Chief — Nephrology
- Section Editor — Fluid and Electrolytes
- Professor Emeritus
- University of Rochester School of Medicine and Dentistry
Calculation of the creatinine clearance to estimate glomerular filtration rate (GFR) is based upon the fact that creatinine is freely filtered and not reabsorbed. Thus, if creatinine secretion is ignored, all of the filtered creatinine (equal to the product of the GFR and the serum creatinine concentration [SCr]) is equal to all of the excreted creatinine (equal to product of the urine creatinine concentration [UCr] and the urine flow rate). Thus:
GFR x SCr = UCr x V
GFR = [UCr x V]/SCr
If muscle mass remains constant, then creatinine production and therefore creatinine excretion (UCr x V) will be relatively constant. Thus, the last equation can be simplified to the GFR being directly proportional to the reciprocal of the serum creatinine concentration. In the clinic, monitoring the reciprocal serum creatinine concentration over time is an effective means of evaluating temporal changes in renal function.
The methods required to use the reciprocal serum creatinine concentration to follow changes in renal function over time will be reviewed here. A graph is also provided to help the clinician in performing this task. A detailed discussion of the use of the serum creatinine concentration and the creatinine clearance to estimate GFR, including drugs that interfere with either creatinine secretion or the assay used to measure the serum creatinine, is presented separately. (See "Assessment of kidney function".)
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