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Test ID: CRC    
Creatinine Clearance, Serum and 24-Hour Urine

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Useful For Suggests clinical disorders or settings where the test may be helpful

Estimation of glomerular filtration rate

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Glomerular filtration rate (GFR) is the sum of filtration rates in all functioning nephrons and so an estimation of the GFR provides a measure of functioning nephrons of the kidney. A decrease in GFR implies either progressive renal disease, or a reversible process causing decreased nephron function (eg, severe dehydration). One of the most common methods used for estimating GFR is creatinine clearance.

 

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. However, approximately 15% of excreted urine creatinine is derived from proximal tubular secretion. Because of the tubular secretion of creatinine, the creatinine clearance typically overestimates the true GFR by 10% to 15%.

 

Creatinine clearance is usually determined from measurement of creatinine in a 24-hour urine specimen and from a serum specimen obtained during the same collection period. The creatinine clearance is then calculated by the equation:

 

2.54 cm=1 inch

1 kg=2.2 pounds (lbs)

Patient surface area (SA)=wt (kg)(.425) X ht (cm)(.725) X 0.007184

 

                                    Urine conc (mg/dL) x 24 hr Urine volume (mL)                                     

Uncorr creat clear=                                                1440 minutes_____    =mL/min

                                                          Plasma creat (mg/dL)       

 

 

                                 Urine conc (mg/dL) x 24 hr urine volume (mL)

Corr creat clear=                                        1440 minutes_______ x 1.73m(2)=

mL/min/1.73m(2)

                                                     Plasma creat (mg/dL)                   Patient SA

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Creatinine Clearance:

Males:

0-18 years: Reference values have not been established

19-75 years: 77-160 mL/min/BSA

> or =76 years: Reference values have not been established

Females:

0-17 years: Reference values have not been established

18-29 years: 78-161 mL/min/BSA

30-39 years: 72-154 mL/min/BSA

40-49 years: 67-146 mL/min/BSA

50-59 years: 62-139 mL/min/BSA

60-72 years: 56-131 mL/min/BSA

> or =73 years: Reference values have not been established

Creatinine, Urine: reported in units of mg/dL

 

Creatinine, Serum

Males

12-24 months: 0.1-0.4 mg/dL

3-4 years: 0.1-0.5 mg/dL

5-9 years: 0.2-0.6 mg/dL

10-11 years: 0.3-0.7 mg/dL

12-13 years: 0.4-0.8 mg/dL

14-15 years: 0.5-0.9 mg/dL

> or =16 years: 0.8-1.3 mg/dL

Reference values have not been established for patients that are less than 12 months of age.

Females

13-36 months: 0.1-0.4 mg/dL

4-5 years: 0.2-0.5 mg/dL

6-8 years: 0.3-0.6 mg/dL

9-15 years: 0.4-0.7 mg/dL

> or =16 years: 0.6-1.1 mg/dL

Reference values have not been established for patients that are less than 12 months of age.

Interpretation Provides information to assist in interpretation of the test results

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 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.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

One of the major limitations of creatinine clearance is erroneous results due to incomplete urine collections. Accurate results depend upon a complete and accurately timed collection.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Post TW, Rose BD: Assessment of renal function: plasma creatinine; BUN; and GFR. In UpTo Date 9.1. Edited by BD Rose. 2001

2. Kasiske BL, Keane WF: Laboratory assessment of renal disease: clearance, urinalysis, and renal biopsy. In The Kidney. Sixth edition. Edited by BM Brenner. Philadelphia, WB Saunders Company, 2000, pp 1129-1170