Creatinine Clearance & Urea-N Clearance (U-24 hrs)
Use of an estimating or prediction equation to estimate GFR from serum creatinine should be employed for people with chronic kidney disease (CKD) and those with risk factors for CKD (diabetes, hypertension, cardiovascular disease, and family history of kidney disease)
Creatinine is derived from the metabolism of creatine from skeletal muscle and dietary meat intake, and is released into the circulation at a relatively constant rate. Thus, the serum creatinine concentration is usually stable. Creatinine is freely filtered by glomeruli and not reabsorbed or metabolized by renal tubules. Therefore, creatinine clearance can be used to assess GFR. However, approximately 15% of excreted urine creatinine is derived from proximal tubular secretion. Because of the tubular secretion of creatinine, creatinine clearance typically overestimates true GFR by 10% to 15%.
Decreased creatinine clearance indicates decreased glomerular filtration rate (GFR). This can be due to conditions such as progressive renal disease, or result from adverse effect on renal hemodynamics that are often reversible, including drug effects or decreases in effective renal perfusion (eg, volume depletion, heart failure).
Increased creatinine clearance is often referred to as hyperfiltration and is most commonly seen during pregnancy or in patients with early diabetes mellitus, before diabetic nephropathy has occurred. It may also occur with large dietary protein intake.
A major limitation of creatinine clearance is that its accuracy worsens in relation to the amount of tubular creatinine secretion. Often as GFR declines, the contribution of urine creatinine from tubular secretion increases, further increasing the discrepancy between true GFR and measured creatinine clearance.
- Manufacturer’s reagent package insert, Architect ® Creatinine (enzymatic), SENTINEL CH.SpA Via Robert Koch, 2 Milan 20152, Italy, March 2017.
- http://www.mayomedicallaboratories.com (Retrieved: 01 Jan 2019)
- Manufacturer’s reagent package insert, Architect ® Urea Nitrogen, Abbott Laboratories Diagnostics Division, Aboott Park, IL 600064, USA. November 2015.